arXiv subjects

Jan Zaanen

Publications and source records attributed to Jan Zaanen.

At least 19 recordsLinked to original sources

arXiv2024

Colossal magnetoresistance from spin-polarized polarons in an Ising system

Recent experiments suggest a new paradigm towards novel colossal magnetoresistance (CMR) in a family of materials EuM$_2$X$_2$(M=Cd, In, Zn; X=P, As), distinct from the traditional avenues involving Kondo-RKKY crossovers, magnetic phase transitions with structural distortions, or topological phase transitions. Here, we use angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations to explore their origin, particularly focusing on EuCd$_2$P$_2$. While the low-energy spectral weight royally tracks that of the resistivity anomaly near the temperature with maximum magnetoresistance (T$_{MR}$) as expected from transport-spectroscopy correspondence, the spectra are completely incoherent and strongly suppressed with no hint of a Landau quasiparticle. Using systematic material and temperature dependence investigation complemented by theory, we attribute this non-quasiparticle caricature to the strong presence of entangled magnetic and lattice interactions, a characteristic enabled by the $p$-$f$ mixing. Given the known presence of ferromagnetic clusters, this naturally points to the origin of CMR being the scattering of spin-polarized polarons at the boundaries of ferromagnetic clusters. These results are not only illuminating to investigate the strong correlations and topology in EuCd$_2$X$_2$ family, but, in a broader view, exemplify how multiple cooperative interactions can give rise to extraordinary behaviors in condensed matter systems.

cond-mat.str-el↗

arXiv2023

T-linear resistivity, optical conductivity and Planckian transport for a holographic local quantum critical metal in a periodic potential

High $T_c$ cuprate strange metals are noted for a DC-resistivity that scales linearly with $T$ from the onset of superconductivity to the crystal melting temperature, indicative of a Planckian dissipation life time $τ_{\hbar}\simeq \hbar /(k_B T)$. At the same time, the optical conductivity ceases to be of Drude form at high temperatures, suggesting a change of the underlying dynamics that surprisingly leaves the $T$-linear DC-resistivity unaffected. We use the AdS/CFT correspondence that describes strongly coupled, densely entangled metals to study DC thermo-electrical transport and the optical conductivities of the local quantum critical Gubser-Rocha holographic strange metal in the presence of a lattice potential, a prime candidate to compare with experiment. We find that the DC-resistivity is linear in $T$ at low temperatures for a range of lattice strengths and wavevectors, even as it transitions between different dissipative regimes. At weak lattice potential the optical conductivity evolves with increasing temperature from a Drude form to a bad-metal characterized by a mid-IR resonance without changing the DC transport, similar to that seen in cuprate strange metals. This mid-IR peak and its temperature evolution can be understood as a consequence of Umklapp hydrodynamics: hydrodynamic perturbations are Bloch modes in the presence of a lattice. At strong lattice potential an incoherent metal is realized instead where momentum conservation no longer plays a role in transport. In this regime the thermal diffusivity can be explained by Planckian dissipation originating in universal microscopic chaos, similar to holographic metals with strong homogeneous momentum relaxation. The charge diffusivity does not submit to this chaos explanation, even though the continuing linear-in-$T$ DC resistivity saturates to an apparent universal slope, numerically equal to a Planckian rate.

cond-mat.str-el↗

arXiv2023

Replicating Higgs fields in Ising gauge theory: the registry order

We consider $Z_2$ gauge field theory coupled to "Higgs" matter fields invoking several copies of such matter, interacting entirely through the gauge fields, the $Z_2 \times Z_2 \times Z_2\cdots / Z_2$ and the $O(N) \times O(N) \times O(N) \cdots / Z_2$ families of theories. We discover that the Higgs phase of such theories is characterized by a hitherto unidentified "registry" order parameter. This is characterized by a gauge invariant $p = 2^{N_{\text{rep}}}/2$ Potts type symmetry where $N_{\text{rep}}$ is the number of matter copies. The meaning of this registry is that the different matter copies align their vectors locally in strictly parallel or anti-parallel fashion, even dealing with the continuous $O(2)$ symmetry. Supported by Monte-Carlo simulations, we identify the origin of this registry order in terms of the gauge interactions mediated by the fluxes ("visons") associated with the $Z_2$ gauge fields, indirectly imposing the discrete symmetry in the gauge invariant global symmetry controlled effective order parameter theory. In addition, it appears that our simulations reveal a hitherto unidentified "pseudo-universality" associated with the very similar form of the overall phase diagrams of the various theories suggesting a remarkable "governance" by the gauge field part of the dynamics.

cond-mat.stat-mech↗

arXiv2022

Motion of a superfluid vortex according to holographic quantum dissipation

Vortices are topological defects associated with superfluids and superconductors, which, when mobile, dissipate energy destroying the dissipation-less nature of the superfluid. The nature of this "quantum dissipation" is rooted in the quantum physical nature of the problem, which has been subject of an extensive literature. However, this has mostly be focused on the measures applicable in weakly interacting systems wherein they are tractable via conventional methods. Recently it became possible to address such dynamical quantum thermalization problems in very strongly interacting systems using the holographic duality discovered in string theory, mapping the quantum problem on a gravitational problem in one higher dimension, having as benefit offering a more general view on how dissipation emerges from such intricate quantum physical circumstances. We study here the elementary problem of a single vortex in two space dimensions, set in motion by a sudden quench in the background superflow formed in a finite density "Reissner-Nordstrom" holographic superconductor. This reveals a number of surprising outcomes addressing questions of principle. By fitting the trajectories unambiguously to the Hall-Vinen-Iordanskii phenomenological equation of motion we find that these are characterized by a large inertial mass at low temperature that however diminishes upon raising temperature. For a weak drive the drag is found to increase when temperature is lowered which reveals a simple shear drag associated with the viscous metallic vortex cores, supplemented by a conventional normal fluid component at higher temperatures. For a strong drive we discover a novel dynamical phenomenon: the core of the vortex deforms accompanied by a large increase of the drag force.

hep-th↗

arXiv2022

Identification of a Critical Doping for Charge Order Phenomena in Bi-2212 Cuprates via RIXS

Identifying quantum critical points (QCPs) and their associated fluctuations may hold the key to unraveling the unusual electronic phenomena observed in cuprate superconductors. Recently, signatures of quantum fluctuations associated with charge order (CO) have been inferred from the anomalous enhancement of CO excitations that accompany the reduction of the CO order parameter in the superconducting state. To gain more insight about the interplay between CO and superconductivity, here we investigate the doping dependence of this phenomenon throughout the Bi-2212 cuprate phase diagram using resonant inelastic x-ray scattering (RIXS) at the Cu L3- edge. As doping increases, the CO wavevector decreases, saturating at a commensurate value of 0.25 r.l.u. beyond a characteristic doping pc, where the correlation length becomes shorter than the apparent periodicity (4a0). Such behavior is indicative of the fluctuating nature of the CO; and the proliferation of CO excitations in the superconducting state also appears strongest at pc, consistent with expected behavior at a CO QCP. Intriguingly, pc appears to be near optimal doping, where the superconducting transition temperature Tc is maximal.

cond-mat.supr-con↗

arXiv2022

Puddle formation, persistent gaps, and non-mean-field breakdown of superconductivity in overdoped (Pb,Bi)2Sr2CuO6+δ

The cuprate high-temperature superconductors exhibit many unexplained electronic phases, but it was often thought that the superconductivity at sufficiently high doping is governed by conventional mean-field Bardeen-Cooper-Schrieffer (BCS) theory[1]. However, recent measurements show that the number of paired electrons (the superfluid density) vanishes when the transition temperature Tc goes to zero[2], in contradiction to expectation from BCS theory. The origin of this anomalous vanishing is unknown. Our scanning tunneling spectroscopy measurements in the overdoped regime of the (Pb,Bi)2Sr2CuO6+δ high-temperature superconductor show that it is due to the emergence of puddled superconductivity, featuring nanoscale superconducting islands in a metallic matrix[3,4]. Our measurements further reveal that this puddling is driven by gap filling, while the gap itself persists beyond the breakdown of superconductivity. The important implication is that it is not a diminishing pairing interaction that causes the breakdown of superconductivity. Unexpectedly, the measured gap-to-filling correlation also reveals that pair-breaking by disorder does not play a dominant role and that the mechanism of superconductivity in overdoped cuprate superconductors is qualitatively different from conventional mean-field theory.

cond-mat.supr-con↗

arXiv2022

Strange metal dynamics across the phase diagram of Bi$_{2}$Sr$_{2}$CuO$_{6+δ}$ cuprates

Unlocking the mystery of the strange metal state has become the focal point of high T$_{c}$ research, not because of its importance for superconductivity, but because it appears to represent a truly novel phase of matter dubbed `quantum supreme matter'. Detected originally through high magnetic field, transport experiments, signatures of this phase have now been uncovered with a variety of probes. Our high resolution optical data of the low T$_{c}$ cuprate superconductor, Bi$_{2-x}$Pb$_{x}$Sr$_{2-y}$La$_{y}$CuO$_{6+δ}$ allows us to probe this phase over a large energy and temperature window. We demonstrate that the optical signatures of the strange metal phase persist throughout the phase diagram. The strange metal signatures in the optical conductivity are two-fold, (i): a low energy Drude response with Drude width on the order of temperature and (ii): a high energy conformal tail with doping dependent power-law exponent. While the Drude weight evolves monotonously throughout the entire doping range studied, the spectral weight contained in the high energy conformal tail appears to be doping and temperature independent. Our analysis further shows that the temperature dependence of the optical conductivity is completely determined by the Drude parameters. Our results indicate that there is no critical doping level inside the superconducting dome where the carrier density starts to change drastically and that the previously observed 'return to normalcy' is a consequence of the increasing importance of the Drude component relative to the conformal tail with doping. Importantly, both the doping and temperature dependence of the resistivity are largely determined by the Drude width.

cond-mat.str-el↗

arXiv2022

Crystal gravity

We address a subject that could have been analyzed century ago: how does the universe of general relativity look like when it would have been filled with solid matter? Solids break spontaneously the translations and rotations of space itself. Only rather recently it was realized in various context that the order parameter of the solid has a relation to Einsteins dynamical space time which is similar to the role of a Higgs field in a Yang-Mills gauge theory. Such a "crystal gravity" is therefore like the Higgs phase of gravity. The usual Higgs phases are characterized by a special phenomenology. A case in point is superconductivity exhibiting phenomena like the Type II phase, characterized by the emergence of an Abrikosov lattice of quantized magnetic fluxes absorbing the external magnetic field. What to expect in the gravitational setting? The theory of elasticity is the universal effective field theory associated with the breaking of space translations and rotations having a similar status as the phase action describing a neutral superfluid. A geometrical formulation appeared in its long history, similar in structure to general relativity, which greatly facilitates the marriage of both theories. With as main limitation that we focus entirely on stationary circumstances -- the dynamical theory is greatly complicated by the lack of Lorentz invariance -- we will present a first exploration of a remarkably rich and often simple physics of "Higgsed gravity".

gr-qc↗

arXiv2022

Spin Texture in Doped Mott Insulators with Spin-Orbit Coupling

A hole injected into a Mott insulator will gain an internal structure as recently identified by exact numerics, which is characterized by a nontrivial quantum number whose nature is of central importance in understanding the Mott physics. In this work, we show that a spin texture associated with such an internal degree of freedom can explicitly manifest after the spin degeneracy is lifted by a \emph{weak} Rashba spin-orbit coupling (SOC). It is described by an emergent angular momentum $J_{z}=\pm3/2$ as shown by both exact diagonalization (ED) and variational Monte Carlo (VMC) calculations, which are in good agreement with each other at a finite size. In particular, as the internal structure such a spin texture is generally present in the hole composite even at high excited energies, such that a corresponding texture in momentum space, extending deep inside the Brillouin zone, can be directly probed by the spin-polarized angle-resolved photoemission spectroscopy (ARPES). This is in contrast to a Landau quasiparticle under the SOC, in which the spin texture induced by SOC will not be protected once the excited energy is larger than the weak SOC coupling strength, away from the Fermi energy. We point out that the spin texture due to the SOC should be monotonically enhanced 1with reducing spin-spin correlation length in the superconducting/pseudogap phase at finite doping. A brief discussion of a recent experiment of the spin-polarized ARPES will be made.

cond-mat.str-el↗

arXiv2021

Lectures on quantum supreme matter

These notes are based on lectures serving the advanced graduate education of the Delta Institute of Theoretical Physics in the Netherlands in autumn 2021. The goal is to explain in a language that can be understood by non-specialists very recent advances in quantum information and especially string theory suggesting the existence of entirely new forms of matter. These are metallic states characterized by an extremely dense many body entanglement, requiring the supremacy of the quantum computer to be completely enumerated. The holographic duality discovered in string theory appears to be a mathematical machinery capable of computing observable properties of such matter, suggesting the presence of universal general principles governing its phenomenology. The case is developing that these principles may well apply to the highly mysterious physical properties observed in the high temperature superconductors and other strongly interacting electron systems of condensed matter physics.

cond-mat.str-el↗

arXiv2021

Holographic Abrikosov lattice: vortex matter from black hole

The AdS/CFT correspondence provides a unique way to study the vortex matter phases in superconductors. We solved the nonlinear equations of motion for the Abelain-Higgs theory living on the AdS$_4$ black hole boundary that is dual to a two dimensional strongly coupled type II superconductor at temperature $T$ with a perpendicular external uniform magnetic field $B_0$. We found the associated two critical magnetic fields, $B_{c1}(T)$ and $B_{c2}(T)$. For $B_0 < B_{c1}(T)$ the magnetic field will be expelled out by the superconductor resembling the Meissner effect and the superconductivity will be destroyed when $B_0 > B_{c2}(T)$. The Abrikosov lattice appears in the range $B_{c1}(T) < B_0 < B_{c2}(T)$ including, due to the finite size and boundary effect, several kinds of configurations such as hexagonal, square and slightly irregular square lattices, when the magnetic field is increased. The upper and lower critical fields behave as inverse squares of coherence length and magnetic penetration depth respectively which matches the well known consensus.

hep-th↗

arXiv2021

Intrinsic one-dimensional conducting channels in the Kondo insulator SmB6

Since its discovery as a Kondo insulator 50 years ago, SmB6 recently received a revival of interest due to detection of unexpected quantum oscillations in the insulating state, discovery of disorder-immune bulk transport, and proposals of correlation-driven topological physics. While recent transport results attribute the anomalous low temperature conduction to two-dimensional surface states, important alternatives, such as conduction channel residing in one-dimensional dislocation lines, have not been adequately explored. Here we study SmB6 with scanning microwave impedance microscopy and uncover evidence for conducting one-dimensional states terminating at surface step edges. These states remain conducting up to room temperature, indicating unusual robustness against scattering and an unconventional origin. Our results bring to light a heretofore undetected conduction route in SmB6 that contributes to the low temperature transport. The unique scenario of intrinsic one-dimensional conducting channels in a highly insulating correlated bulk offers a one-dimensional platform that may host exotic physics.

cond-mat.str-el↗

arXiv2021

Electronic Structure Trends Across the Rare-Earth Series in Superconducting Infinite Layer Nickelates

The recent discovery of superconductivity in oxygen-reduced monovalent nickelates has raised a new platform for the study of unconventional superconductivity, with similarities and differences with the cuprate high temperature superconductors. In this paper we investigate the family of infinite-layer nickelates $R$NiO$_2$ with rare-earth $R$ spanning across the lanthanide series, introducing a new and non-trivial "knob" with which to tune nickelate superconductivity. When traversing from La to Lu, the out-of-plane lattice constant decreases dramatically with an accompanying increase of Ni $ d_{x^2-y^2}$ bandwidth; however, surprisingly, the role of oxygen charge transfer diminishes. In contrast, the magnetic exchange grows across the lanthanides which may be favorable to superconductivity. Moreover, compensation effects from the itinerant $5d$ electrons present a closer analogy to Kondo lattices, indicating a stronger interplay between charge transfer, bandwidth renormalization, compensation, and magnetic exchange. We also obtain the microscopic Hamiltonian using Wannier downfolding technique, which will provide the starting point for further many-body theoretical studies.

cond-mat.supr-con↗

arXiv2019

Isolated zeros destroy Fermi surface in holographic models with a lattice

We study the fermionic spectral density in a strongly correlated quantum system described by a gravity dual. In the presence of periodically modulated chemical potential, which models the effect of the ionic lattice, we explore the shapes of the corresponding Fermi surfaces, defined by the location of peaks in the spectral density at the Fermi level. We find that at strong lattice potentials sectors of the Fermi surface are unexpectedly destroyed and the Fermi surface becomes an arc-like disconnected manifold. We explain this phenomenon in terms of a collision of the Fermi surface pole with zeros of the fermionic Green's function, which are explicitly computable in the holographic dual.

hep-th↗

arXiv2019

Thermalization/Relaxation in integrable and free field theories: an Operator Thermalization Hypothesis

Free or integrable theories are usually considered to be too constrained to thermalize. For example, the retarded two-point function of a free field, even in a thermal state, does not decay to zero at long times. On the other hand, the magnetic susceptibility of the critical transverse field Ising is known to thermalize, even though that theory can be mapped by a Jordan-Wigner transformation to that of free fermions. We reconcile these two statements by clarifying under which conditions conserved charges can prevent relaxation at the level of linear response and how such obstruction can be overcome. In particular, we give a necessary condition for the decay of retarded Green's functions. We give explicit examples of composite operators in free theories that nevertheless satisfy that condition and therefore do thermalize. We call this phenomenon the Operator Thermalization Hypothesis as a converse to the Eigenstate Thermalization Hypothesis.

cond-mat.stat-mech↗

arXiv2019

Ground state phase diagram of the doped Hubbard model on the 4-leg cylinder

We study the ground state properties of the Hubbard model on a 4-leg cylinder with doped hole concentration per site $δ\leq 12.5\%$ using density-matrix renormalization group. By keeping a large number of states for long system sizes, we find that the nature of the ground state is remarkably sensitive to the presence of next-nearest-neighbor hopping $t'$. Without $t'$ the ground state of the system corresponds with the insulating filled stripe phase with long-range charge-density-wave (CDW) order and short-range incommensurate spin correlations appears. However, for a small negative $t'$ a phase characterized by coexisting algebraic d-wave superconducting (SC)- and algebraic CDW correlations. In addition, it shows short range spin- and fermion correlations consistent with a canonical Luther-Emery (LE) liquid, except that the charge- and spin periodicities are consistent with half-filled stripes instead of the $4 k_F$ and $2 k_F$ wavevectors generic for one dimensional chains. For a small positive $t'$ yet another phase takes over showing similar SC and CDW correlations. However, the fermions are now characterized by a (near) infinite correlation length while the gapped spin system is characterized by simple staggered antiferromagnetic correlations. We will show that this is consistent with a LE formed from a weakly coupled (BCS like) d-wave superconductor on the ladder where the interactions have only the effect to stabilize a cuprate style magnetic resonance.

cond-mat.str-el↗

arXiv2019

Anomalous attenuation of plasmons in strange metals and holography

The plasmon is a ubiquitous collective mode in charged liquids. Due to the long-range Coulomb interaction, the massless zero sound mode of the neutral system acquires a finite plasmon frequency in the long-wavelength limit. In the zero-temperature state of conventional metals -- the Fermi liquid -- the plasmon lives infinitely long at long wavelength when the system is (effectively) translationally invariant. In contrast, we will show that in strongly entangled strange metals the protection of zero sound fails at finite frequency and plasmons are always short lived regardless of their wavelength. Computing the explicit plasmon response in holographic strange metals as an example, we show that decay into the quantum critical continuum replaces Landau damping and this happens for any wavelength.

cond-mat.str-el↗

arXiv2019

Isolated zeros in the spectral function as signature of a quantum continuum

We study the observable properties of quantum systems which involve a quantum continuum as a subpart. We show in a very general way that in any system, which consists of at least two isolated states coupled to a continuum, the spectral function of one of the states exhibits an isolated zero at the energy of the other state. Several examples of quantum systems exhibiting such isolated zeros are discussed. Although very general, this phenomenon can be particularly useful as an indirect detection tool for the continuum spectrum in the lab realizations of quantum critical behavior.

cond-mat.str-el↗