A recent advance in the study of emergent magnetic monopoles was the discovery that monopole motion is restricted to dynamical fractal trajectories thus explaining the anomalous color of magnetic monopole noise spectra. Applying these novel concepts to fielddriven magnetic monopole currents predicts a characteristic dichotomy in both their DC and AC dynamics. To explore these novel perspectives on monopole transport, we introduce simultaneous monopole current control and measurement techniques using SQUIDbased monopole current sensors. For the canonical material Dy_{2}Ti_{2}O_{7}, we measure φ(t), the timedependence of magnetic flux threading the sample when a net monopole current J(t)=φ(t)/μ_{0} is generated by applying an external magnetic field B_{0}(t). These experiments find a sharp dichotomy of monopole currents, separated by their distinct relaxation timeconstants before and after t∼600 μs from monopole current initiation. Application of sinusoidal magnetic fields B_{0}(t)=Bcos(ωt) generates oscillating monopole currents whose loss angle θ(f) exhibits a characteristic transition at frequency f≈1.8 kHz over the same temperature range. Finally, the magnetic noise power is also dichotomic, diminishing sharply after t∼600 μs. An accurate atomicscale understanding of the mechanisms of magnetic monopole currents in spinice is thereby established. This complex phenomenology represents a new form of heterogeneous dynamics generated by the interplay of fractionalization and local spin configurational symmetry.  
published article 

No state of matter can be defined categorically by what it is not; yet spin liquids are often conjectured to exist based on the nonexistence of magnetic order as T→0. An emerging concept designed to circumvent this ambiguity is to categorically identify each spin liquid type by using its spectrum of spontaneous spin noise. Here we introduce such a spectroscopy to spin liquid studies by considering Ca_{10}Cr_{7}O_{28}. This is a spin liquid, but whether classical or quantum and in which specific state, are unknown. By enhancing the fluxnoise spectrometry techniques introduced for magnetic monopole noise studies, here we measure the time and temperature dependence of spontaneous flux φ(t,T) and thus magnetization M(t,T) of Ca_{10}Cr_{7}O_{28} samples. The resulting power spectral density of magnetization noise S_{M}(ω,T) along with its correlation function C_{M}(t,T), reveal intense spin fluctuations spanning frequencies 0.1Hz ≤ ω/2π ≤ 50kHz, and that S_{M}(ω,T)∝ω^{α(T)} with 0.84<α(T)<1.04. Predictions for quantum spin liquids yield a frequencyindependent spinnoise spectrum, clearly inconsistent with this phenomenology. However, when compared to Monte Carlo simulations for a 2D spiral spin liquid state that are accurately parameterized to describe Ca_{10}Cr_{7}O_{28}, comprehensive quantitative correspondence with the data including S_{M}(ω,T), C_{M}(t,T) and magnetization variance σ_{M}^{2}(T) fingerprint the state of Ca_{10}Cr_{7}O_{28} as a spiral spin liquid.  
published article 

The primordial ingredient of cuprate superconductivity is the CuO_{2} unit cell. Theories usually concentrate on the intraatom Coulombic interactions dominating the 3d^{9} and 3d^{10} configurations of each copper ion. However, if Coulombic interactions also occur between electrons of the 2p^{6} orbitals of each planar oxygen atom, spontaneous orbital ordering may split their energy levels. This longpredicted intraunitcell symmetry breaking should generate an orbitally ordered phase, for which the charge transfer energy ε separating the 2p^{6} and 3d^{10} orbitals is distinct for the two oxygen atoms. Here we introduce sublatticeresolved ε(r) imaging to CuO_{2} studies and discover intraunitcell rotational symmetry breaking of ε(r). Spatially, this state is arranged in disordered Ising domains of orthogonally oriented orbital order bounded by dopant ions, and within whose domain walls lowenergy electronic quadrupolar twolevel systems occur. Overall, these data reveal a Q=0 orbitally ordered state that splits the oxygen energy levels by ∼50meV, in underdoped CuO_{2}.  
published article 

The properties of superconducting materials, their perfectly dissipationless electronics, perfect diamagnetism, and macroscopic quantum mechanical dynamics are all the products of the formation of a macroscopic quantum fluid of electron pairs. To better understand this, we have developed the first scanned Josephson/Andreev tunneling microscopes (SJTM/SATM) which provide direct access to the macroscopic quantum electron pair condensate. Since the 1960s the possibility of a crystalline superconducting phase within the overall fluid has been discussed with great interest in the superconducting community. Such a state should manifest itself as a spatially periodic electronpair crystal; we call this state a Pair Density Wave (PDW). For years the superconducting community had suggested that such a PDW state might exist in the hightemperature superconductor Bi_{2}Sr_{2}CaCu_{2}O_{8+x}. In 2016 our group developed our first SJTM system and subsequently detected this long predicted PDW state. Since then we have discovered PDWs in several other materials including in the transition metal dichalcogenide superconductor NbSe_{2}. Recently our focus of study has been the spintriplet topological superconductor UTe_{2}. This class of superconductor should exhibit many unprecedented electronic properties including fractionalized electronic states relevant to quantum information processing. In UTe_{2} we searched for a PDW state, by visualizing the pairing energygap with μeVscale energyresolution made possible by a superconducting SATM tip. We discovered three PDWs at incommensurate wavevectors P_{i} = 1,2,3 that are indistinguishable from the wavevectors Q_{i} = 1,2,3 of the prevenient CDW. From these observations and given UTe_{2} as a spintriplet superconductor, this PDW state appears to be the first known spintriplet pair density wave. 

published article 

A Kondo lattice is often electrically insulating at low temperatures. However, several recent experiments have detected signatures of metallicity within this Kondo insulating phase. In this study, we visualized the realspace charge landscape within a Kondo lattice with atomic resolution using a scanning tunneling microscope. We discovered nanometerscale puddles of metallic conduction electrons centered around uraniumsite substitutions in the heavyfermion compound uranium ruthenium silicide (URu_{2}Si_{2}) and around samariumsite defects in the topological Kondo insulator samarium hexaboride (SmB_{6}). These defects disturbed the Kondo screening cloud, leaving behind a fingerprint of the metallic parent state. Our results suggest that the threedimensional quantum oscillations measured in SmB_{6} arise from Kondolattice defects, although we cannot exclude other explanations.  
published article 

The elementary CuO_{2} plane sustaining cuprate hightemperature superconductivity occurs typically at the base of a periodic array of edgesharing CuO_{5} pyramids. Virtual transitions of electrons between adjacent planar Cu and O atoms, occurring at a rate t/ℏ and across the chargetransfer energy gap ε, generate “superexchange” spin–spin interactions of energy J ≈ 4t^{4}/ε^{3} in an antiferromagnetic correlatedinsulator state. However, hole doping this CuO_{2} plane converts this into a veryhightemperature superconducting state whose electron pairing is exceptional. A leading proposal for the mechanism of this intense electron pairing is that, while hole doping destroys magnetic order, it preserves pairforming superexchange interactions governed by the chargetransfer energy scale ε. To explore this hypothesis directly at atomic scale, we combine singleelectron and electronpair (Josephson) scanning tunneling microscopy to visualize the interplay of ε and the electronpair density n_{p} in Bi_{2}Sr_{2}CaCu_{2}O_{8+x}. The responses of both ε and n_{p} to alterations in the distance δ between planar Cu and apical O atoms are then determined. These data reveal the empirical crux of strongly correlated superconductivity in CuO_{2}, the response of the electronpair condensate to varying the chargetransfer energy. Concurrence of predictions from strongcorrelation theory for holedoped chargetransfer insulators with these observations indicates that chargetransfer superexchange is the electronpairing mechanism of superconductive Bi_{2}Sr_{2}CaCu_{2}O_{8+x}.  
published article 

Electronpair density wave (PDW) states are now an intense focus of research in the field of cuprate correlated superconductivity. PDWs exhibit periodically modulating superconductive electron pairing that can be visualized directly using scanned Josephson tunneling microscopy (SJTM). Although from theory, intertwining the dwave superconducting (DSC) and PDW order parameters allows a plethora of global electronpair orders to appear, which one actually occurs in the various cuprates is unknown. Here, we use SJTM to visualize the interplay of PDW and DSC states in Bi_{2}Sr_{2}CaCu_{2}O_{8+x} at a carrier density where the charge density wave modulations are virtually nonexistent. Simultaneous visualization of their amplitudes reveals that the intertwined PDW and DSC are mutually attractive states. Then, by separately imaging the electronpair density modulations of the two orthogonal PDWs, we discover a robust nematic PDW state. Its spatial arrangement entails Ising domains of opposite nematicity, each consisting primarily of unidirectional and lattice commensurate electronpair density modulations. Further, we demonstrate by direct imaging that the scattering resonances identifying Zn impurity atom sites occur predominantly within boundaries between these domains. This implies that the nematic PDW state is pinned by Zn atoms, as was recently proposed [Lozano et al., Phys. Rev. B 103, L020502 (2021)]. Taken in combination, these data indicate that the PDW in Bi_{2}Sr_{2}CaCu_{2}O_{8+x} is a vestigial nematic pair density wave state [Agterberg et al. Phys. Rev. B 91, 054502 (2015); Wardh and Granath arXiv:2203.08250].  
published article 

An unidentified quantum fluid designated the pseudogap (PG) phase is produced by electrondensity depletion in the CuO_{2} antiferromagnetic insulator. Current theories suggest that the PG phase may be a pair density wave (PDW) state characterized by a spatially modulating density of electron pairs. Such a state should exhibit a periodically modulating energy gap Δ_{P}(r) in realspace, and a characteristic quasiparticle scattering interference (QPI) signature Λ_{P}(q) in wavevector space. By studying strongly underdoped Bi_{2}Sr_{2}CaDyCu_{2}O_{8} at holedensity ~0.08 in the superconductive phase, we detect the 8a_{0}periodic Δ_{P}(r) modulations signifying a PDW coexisting with superconductivity. Then, by visualizing the temperature dependence of this electronic structure from the superconducting into the pseudogap phase, we find evolution of the scattering interference signature Λ(q) that is predicted specifically for the temperature dependence of an 8a_{0}periodic PDW. These observations are consistent with theory for the transition from a PDW state coexisting with dwave superconductivity to a pure PDW state in the Bi_{2}Sr_{2}CaDyCu_{2}O_{8} pseudogap phase.  
published article 

Pair density wave (PDW) states are defined by a spatially modulating superconductive order parameter. To search for such states in transitionmetal dichalcogenides (TMDs), we used highspeed atomic resolution scanned Josephsontunneling microscopy. We detected a PDW state whose electronpair density and energy gap modulate spatially at the wave vectors of the preexisting charge density wave (CDW) state. The PDW couples linearly to both the swave superconductor and the CDW and exhibits commensurate domains with discommensuration phase slips at the boundaries, conforming those of the latticelocked commensurate CDW. Nevertheless, we found a global δΦ ≈ ±2π/3 phase difference between the PDW and CDW states, possibly owing to the Cooperpair wave function orbital content. Our findings presage pervasive PDW physics in the many other TMDs that sustain both CDW and superconducting states.  
published article 

Although rapid advances have occurred in quantum fluid flow imaging, the velocity field v(r) of a charged superfluid  a superconductor  had never been visualized. We used superconductive–tip scanning tunneling microscopy to image the electronpair density ρ_{s}(r) and velocity v_{s}(r) fields of the flowing electronpair fluid in superconducting NbSe_{2}. Imaging v_{s}(r) surrounding a quantized vortex finds speeds reaching 10,000 km/hr. Together with independent imaging of ρ_{s}(r) via Josephson tunneling, we visualize the supercurrent density j_{s}(r)≡ ρ_{s}(r)v_{s}(r), which peaks above 3×10^{7} A/cm^{2}. The spatial patterns in electronpair fluid flow and magnetohydrodynamics reveal hexagonal structures coaligned to the crystal lattice and quasiparticle bound states, as long anticipated from NbSe_{2} crystal symmetry. This demonstration of atomicscale imaging of v_{s}(r) for charged superfluid paves the way for electronic fluid flow visualization in other quantum fluids.  
published article 

The quantum anomalous Hall (QAH) effect appears in ferromagnetic topological insulators (FMTIs) when a Dirac mass gap opens in the spectrum of the topological surface states (SSs). Unaccountably, although the mean mass gap can exceed 28 meV (or ~320 K), the QAH effect is frequently only detectable at temperatures below 1 K. Using atomicresolution Landau level spectroscopic imaging, we compare the electronic structure of the archetypal FMTI Cr_{0.08}(Bi_{0.1}Sb_{0.9})_{1.92}Te_{3} to that of its nonmagnetic parent (Bi_{0.1}Sb_{0.9})_{2}Te_{3}, to explore the cause. In (Bi_{0.1}Sb_{0.9})_{2}Te_{3}, we find spatially random variations of the Dirac energy. Statistically equivalent Dirac energy variations are detected in Cr_{0.08}(Bi_{0.1}Sb_{0.9})_{1.92}Te_{3} with concurrent but uncorrelated Dirac mass gap disorder. These two classes of SS electronic disorder conspire to drastically suppress the minimum mass gap to below 100 µeV for nanoscale regions separated by <1 µm. This fundamentally limits the fully quantized anomalous Hall effect in Sb_{2}Te_{3}based FMTI materials to very low temperatures.  
published article 

The defining characteristic of Cooper pairs with finite centerofmass momentum is a spatially modulating superconducting energy gap Δ(r). Recently, this concept has been generalized to the pair density wave (PDW) state predicted to exist in high temperature superconducting cuprates (ARCMP 11, 231 (2020) ). Although the existence of a PDW in cuprates was discovered by using Cooperpair tunneling (Nature 532, 343 (2016) ), its signature in singleelectron tunneling of periodic Δ(r) modulations, proved elusive. Now, by using a new approach, we detect strong Δ(r) modulations in Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} that have eightunitcell periodicity or wavevectors Q ≈ 2π/a_{0} (1/8,0); 2π/a_{0} (0,1/8). Simultaneous imaging of the localdensityofstates N(r,E) reveals electronic modulations with wavevectors Q and 2Q, as anticipated for a coexisting superconductor and PDW. Overall, this provides strong confirmation that a PDW state coexists with superconductivity in the canonical cuprate Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}. These results were published in Nature 580, 6570 (April 2020)..  
published article  download PDF 

Magnetic monopoles are highly elusive elementary particles exhibiting quantised magnetic charge. The prospect for studying them has brightened in recent years with the theoretical realisation that, in certain classes of magnetic insulators, the thermally excited states exhibit all the characteristics of magnetic monopoles. Specifically, recent theories predicted that these magnetic insulators should spontaneously generate wildly and randomly fluctuating magnetic fields as the monopoles move around, but with a magnitude near one billionth of the Earth’s field. Using an exquisitely sensitive magneticfieldnoise spectrometer based on a superconducting quantum interference device (SQUID), we detected from crystals of Dy_{2}Ti_{2}O_{7} virtually all the predicted features of the magnetic noise coming from a dense fluid of magnetic monopoles. Extraordinarily, because this magnetic monopole noise occurs in the frequency range below 20kHz, when amplified by the SQUID it is actually audible to humans as exemplified in this video clip.  
published article  download PDF See also  Oxford Science Blog / Phys.org 

A collaboration of experimental physicists led by Prof. JC Séamus Davis (University of Oxford), theoretical physicists led by Prof. EunAh Kim (Cornell University), and computer scientists led by Prof. E. Kathami (San Jose State University), developed and trained a new Machine Learning (ML) protocol, based on a suite of artificial neural networks (ANN), that is designed to recognize different types of electronic ordered states which are hidden within electronic quantum matter imagearrays. Electronic quantum matter studies using automated scientific instrumentation and largescale data acquisition are now generating data sets of such volume and complexity as to defy human analysis. For example modern scanning tunneling microscopy (STM) visualization of electronic quantum matter (EQM) yields dense arrays of atomicscale, electronicstructure images, that are often astonishingly complex. The ANN suite analyzed one of the Davis Group experimental EQM image archives, spanning a wide range of electron densities and energies, in carrierdoped cuprate Mott insulators. The ANN suite discovered, throughout all the noisy and complex data, the features of a very specific ordered state of EQM: a Vestigial Nematic State. This is a milestone for general scientific technique in that ANN’s can process and identify specific broken symmetries of highly complex imagearrays from nonsynthetic experimental EQM data. It opens the immediate prospect of additional MLdriven scientific discovery in EQM studies. 

published article  download PDF See also  Phys.org / Science Daily / EE News Analog 

Superconductivity occurs when electrons form pairs of opposite spin and opposite momentum, and these "Cooper pairs" condense into a homogeneous electronic fluid. However, theorists have recently realized that these electron pairs might also crystallize into a “pair density wave” (PDW) state where the density of pairs modulates periodically in space. Intense theoretical interest has emerged in whether such a PDW is the competing phase in cuprates. To search for evidence of such a PDW state we suppress the homogeneous superconductivity using high magnetic field and visualize the electronic structure of the new phase which appears. Under these circumstances we discovered modulations in the density of electronic states containing multiple signatures of a PDW state. The phenomena are in detailed and excellent agreement with theoretical predictions for a fieldinduced primary PDW state. These data indicate that it is a PDW state which competes with superconductivity in cuprates and that it dominates in the highfield regime.  
published article  download PDF See also  Phys.org / Science Daily / EurekaAlert 

In the cuprate pseudogap phase, an energy gap of unknown mechanism opens, and both an electronic nematic phase (NE) and a densitywave (DW) phase appear. Perplexingly, the DW, which should generate an energy gap, appears without any new gap opening; and the NE, which should be incapable of opening an energy gap, emerges coincident with the pseudogap opening. Recently, however, it was demonstrated theoretically that a disordered unidirectional DW can generate a vestigial nematic (VN) phase. If the cuprate pseudogap phase were in such a VN state, the energy gap of the NE and DW should be identical to each other and to the pseudogap. We report discovery of such a phenomenology throughout the phase diagram of underdoped Bi_{2}Sr_{2}CaCu_{2}O_{8}. (click the image for enlarged version) 

published article  download PDF Commentary by Kivelson & Lederer (PDF) 

Strong electronic correlations, emerging from the parent Mott insulator phase, are key to copperbased hightemperature superconductivity. By contrast, the parent phase of an ironbased hightemperature superconductor is never a correlated insulator. However, this distinction may be deceptive because Fe has five active dorbitals while Cu has only one. In theory, such orbital multiplicity can generate a Hund's metal state, in which alignment of the Fe spins suppresses interorbital fluctuations, producing orbitally selective strong correlations. The spectral weights Zm of quasiparticles associated with different Fe orbitals m should then be radically different. Here we use quasiparticle scattering interference resolved by orbital content to explore these predictions in FeSe. Signatures of strong, orbitally selective differences of quasiparticle Z_{m} appear on all detectable bands over a wide energy range. Further, the quasiparticle interference amplitudes reveal that Z_{xy}<Z_{xz}<<Z_{yz}, consistent with earlier orbitalselective Cooper pairing studies. Thus, orbitalselective strong correlations dominate the parent state of ironbased hightemperature superconductivity in FeSe.  
published article  download PDF News and Views article by Massimo Capone (PDF) See also  BNL News 

The cuprate pseudogap exhibits an unidentified unconventional density modulation, which is widely believed to be charge density wave (CDW). Recent theory indicates that it could actually be an electronpair density wave (PDW) state. Here we demonstrate theoretically that a biaxial PDW state with 8a_{0} periodicity may provide a compelling quantitative explanation for much of the observed quantum oscillation data.  
published article  download PDF (Proc. Nat'l Aacd. Sci. 115, 5389  22 May 2018) 

In Cubased HTS materials, the undoped phase is a robust Mott insulator while, in Febased HTS materials, the undoped phase is generally not an insulator at all. Thus, proximity to a Mott insulator appears neither indispensable nor universal to HTS. However, theory predicts that Febased materials could still be governed by strong electronic correlations proximate to a Mott insulator if an orbital selective Mott phase (OSMP) exists. A key signature of OSMP would be orbital selective Cooper pairing wherein electrons of a specific orbital character predominantly form the Cooper pairs. (click the image for enlarged version) 

published article  download PDF See also  BNL News / Phys.org / Science Daily 

Phaseoptimization analysis of the phaseresolved electronic structure reveals a virtually dopingindependent locking of the local charge density modulation with four crystal unit cell periodicity throughout the underdoped phase diagram of the canonical cuprate Bi_{2}Sr_{2}CaCu_{2}O_{8+x}.  
published article  download PDF


Theory predicts that the cuprate pseudogap phase should contain a spatially modulating Cooperpair density wave (PDW) state. This would be akin to the famous FFLO state of spatially modulated conventional superconductivity, but generated by strong correlations instead of high magnetic fields. To search for a cuprate PDW, we developed a millikelvin scanned Josephson tunneling microscope (SJTM) system that can image Cooperpair tunneling from a dwave superconducting STM tip to the Cooperpair condensate of Bi_{2}Sr_{2}CaCu_{2}O_{8}. Nanometer resolution condensate visualization then revealed a Cooperpair density wave modulating along the CuO bond directions at wavevectors Q_{p} ~ (1/4,0)*2π/a_{0}; (0,1/4)*2π/a_{0}.  
published article  download PDF See also  BNL news / Cornell Chronicle / Phys.org 

Energyresolved sublattice visualization of the electronic structure reveals that the dformfactor density wave states in underdoped cuprate involve particlehole interactions focused at the pseudogap energy scale and between the four pairs of 'hot frontier' regions in momentum space where the pseudogap opens.  
published article  download PDF See also  BNL news / Nanowerk / Phys.org 

A classic "supercooled" liquid develops when a fluid does not crystallize upon cooling below its ordering temperature. Such liquids have specific identifiers including microscopic relaxation times diverging on a VogelTammannFulcher (VTF) trajectory, a HavriliakNegami (HN) form for the dielectric function, and a general KohlrauschWilliamsWatts (KWW) form for timedomain relaxation. Recently, the magnetic state of the frustrated pyrochlore Dy_{2}Ti_{2}O_{7} has become of wide interest. By introducing novel magnetization transport measurement techniques, an improved understanding of the time and frequencydependent magnetization dynamics of Dy_{2}Ti_{2}O_{7} is achieved. We find that this system exhibits a virtually universal HN form for the magnetic susceptibility, a general KWW form for the realtime magnetic relaxation, and a divergence of the microscopic magnetic relaxation rates with the VTF trajectory. Lowtemperature Dy_{2}Ti_{2}O_{7} therefore exhibits all the characteristics expected of a supercooled classical spinliquid; we propose that this is the correct description of its magnetic state.  
published article  download PDF (Proc. Nat'l. Acad. Sci. 112, 8549  Jul 2015) 

SISTM study visualizes the atomicscale effects of irradiating Fe(Se,Te) superconductor with highenergy heavy ions. Simultaneous imaging of defects, superconducting order parameter and vortex configuration reveals how columnar and point defects pin quantum vortices allowing high critical current density. 

published article  download PDF See also  BNL news / Nanowerk / Phys.org 

By introducing the Diracmass 'gapmap' technique, i.e. simultaneously visualizing the mass gap Δ(r) and the ferromagnetic dopant atoms in the atomicscale, we discover intense nanoscale disorder in the Diracmass and demonstrate that this is directly related to fluctuations in the magneticdopant atom density n(r). (click the image for expanded version with scale bars) 

published article  download PDF  movie [wmv] See also  BNL news / Cornell Chronicle 

Quasiparticle Interference (QPI) imaging technique reveals that electronboson interaction in LiFeAs superconductivity has momentumspace anisotropic selfenergy 'fingerprint' of antiferromagnetic spin fluctuations. 

published article  download PDF See also  Phys.org / R&D Magazine 

Direct sublatticephaseresolved imaging of the electronic structure in both Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} and Ca_{2x}Na_{x}CuO_{2}Cl_{2} reveals that the cuprate pseudogap phase exhibits a previously unknown electronic state: a dsymmetry form factor density wave. (click the image for enlarged version) 

published article  download PDF See also  Phys.org / Quanta Magazine 

Quasiparticle interference imaging of heavy fermions reveals the momentumspace structure of the felectron magnetism in CeCoIn_{5}. Using this novel information, we then demonstrate directly and quantitatively that the Cooper pairing in this heavy fermion superconductor is mediated by the felectron magnetic interactions. 

published article  download PDF See also  Science Editor's choice 

Abrupt transition in Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} Fermi surface topology from broken 'arc' to full closed contour is visualized with SISTM to occur at the same critical doping level where dform factor density wave disappears. 

published article  download PDF See also  DoE headliner (click to see captured 

Rich ordering phenomena with distinct symmetry observed in proximity to the superconductivity of Cubased / Febased / heavyfermion compounds are explained in a unified theory based on antiferromagnetic interaction. (Click the image for enlarged version) 

published article  download PDF See also  

Complex band structure and the Fermi surface of CeCoIn_{5} is revealed in detail with QPI. Also visualized for the first time in heavy fermion superconductor compound is the superconducting energy gaps, shown to be consistent with d_{x2y2} symmetry.  
published article  download PDF See also  

Dopantinduced impurity states in underdoped ironbased superconductor Ca(Fe_{1x}Co_{x})_{2}As_{2}, resulting quasiparticle scattering, and its relation to the nematic transport of the parent phase are studied with SISTM and ARPES.


published article  download PDF See also  

Zinc impurity states inside Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} are located to picometer scale, providing phase information for intraunitcell Braggpeak Fourier analysis.  
published article  download PDF (New Journal of Physics 14, 053017  May 2012) 

Anisotropic energy gaps of ironbased superconductor LiFeAs are determined from intraband QPI analysis.  
published article  download PDF See also  

Electronic structure of Kondo holes in the Thdoped heavy Fermion compound URu_{2}Si_{2} is visualized with STM to find heterogeneous hybridization strength in nanoscale.  
published article  download PDF See also  

The 2π topological defects in the pseudogap phase of underdoped Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} and the relationship between the coexistent smectic and intraunitcell broken symmetries are studied.  
published article  download PDF See also  

Interplay of rotational, relaxational and shear dynamics in solid ^{4}He is investigated.  
published article  download PDF See also  

Electronic nematicity within unit cell in Bi_{2}Sr_{2}CaCu_{2}O_{8+δ } was studied with SISTM.  
published article  download PDF 

Heavyfermion compound URu_{2}Si_{2} is investigated in both real and momentum space with spectroscopic imaging (SI)  STM.  
published article  download PDF (Nature 465, 570  June 2010) See also  News and Views by A. J. Schofield (Nature 465, 553) 

Nematic electronic structure in the parent state of the ironbased superconductor Ca(Fe_{1x}Co_{x})_{2}As_{2} is revealed by spectroscopic imaging (SI) STM measurements in both realspace and momentumspace.  
published article  download PDF 

Heavy delectron quasiparticle interferenc(QPI) patterns in kspace and subatomic electronic structure in rspace are revealed by spectroscopic imaging(SI) STM measurements on Sr_{3}Ru_{2}O_{7}. A relevant band is also identified from the complicated band structure of Sr_{3}Ru_{2}O_{7} by inverting dispersing QPI patterns.  
published article  download pdf 

Quasiparticle interference imaging in the cuprate pseudogap state (T>Tc) reveals the spectroscopic 'fingerprint' of phase incoherent dwave superconductivity. (Click image to enlarge)  
published article  download PDF See also  

Relaxation study of ^{4}He in the solid phase reveals ultraslow dynamics, evidencing the formation of superglass state. 

published article  download PDF 

Investigation of the vanishing pattern of Cooper pairs in Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}, approaching the Mott insulator.  
published article  download PDF 

Evolution of the electronic excitation spectrum with strongly diminishing hole density in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}.  
published article  download PDF (Nature Physics 4, 319  Apr 2008) See also  review by Eric Hudson (Nature Physics 4, 271) 

Imaging the impact on cuprate superconductivity of varying the interatomic distances within individual crystal cells .  
published article  download PDF 

Quasiparticle interference of nearly optimally doped Ca_{2x}Na_{x}CuO_{2}Cl_{2} was studied using STS.  
published article  download PDF  
Atomic resolution tunneling asymmetry imaging: an intrinsic CuOCu bondcentered electronic glass with disperse 4a_{0}wide unidirectional domains in underdoped Ca_{1.88}Na_{0.12}CuO_{2}Cl_{2} and Bi_{2}Sr_{2}Dy_{0.2}Ca_{0.8}Cu_{2}O_{8+δ}  
published article  cover story  download PDF (Science 315, 1380  Mar 2007) Click the left image to see the movie. 

The pseudogap state in cuprate superconductors La_{2x}Ba_{x}CuO_{4} (x=1/8) was studied by ARPES and STM.  
published article  download PDF (Science 314, 1914  Dec 2006) 

The influence of atomic scale electronlattice interactions on highT_{c} superconductivity was imaged by STM.  
published article  download PDF (Nature 442, 546  Aug 2006) 

Atomicscale sources and mechanism of nanoscale electronic disorder in Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} were identified by STM.  
published article  download PDF (Science 309, 1048  Aug 2005) 

The doping dependence of nanoscale electronic structure in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} was studied by STM.  
published article  download PDF (Phys. Rev. Lett. 94, 197005  May 2005) 

'Checkerboard' electronic crystal state in the lightly holedoped cuprate Ca_{2x}Na_{x}CuO_{2}Cl_{2}.  
published article  download PDF (Nature 430, 1001  Aug 2004) See also : Magnetic Material Laboratory site (RIKEN) Physics Today  cover figure by Curry Taylor 

The relationship between atomicscale electronic phenomena and wavelike quasiparticle states in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+δ } was explained in terms of an octet model of quasiparticle interference.  
published article  download PDF (Nature 422, 592  Apr 2003) 

The granular structure of highT_{c} superconductivity in underdoped Bi_{2}Sr_{2}CaCu_{2}O_{8+δ } was imaged with atomic resolution, revealing inherent heterogeneity.  
published article  download PDF (Nature 415, 412  Jan 2002) 

A checkerboardlike Four Unit Cell Periodic Pattern of QuasiParticle States Surrounding Vortex Cores in Bi_{2}Sr_{2}CaCu_{2}O_{8+δ } was discovered.  
published article  download PDF (Science 295, 466  Jan 2002) 

. 