High-Tc cuprate strange metals are characterized by a DC resistivity that scales linearly with T from the onset of superconductivity to the crystal melting temperature, characterized by a current... Show moreHigh-Tc cuprate strange metals are characterized by a DC resistivity that scales linearly with T from the onset of superconductivity to the crystal melting temperature, characterized by a current life time τℏ≃ℏ/(kBT), the “Planckian dissipation”. At the same time, the optical conductivity ceases to be of the 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 many-body entangled metallic states of matter to study the DC thermoelectrical transport properties and the optical conductivities of the local quantum critical Gubser-Rocha holographic strange metal in 2+1 dimensions in the presence of a lattice potential, a prime candidate to compare with experiment. We find that the electrical DC resistivity is linear in T at low temperatures for a large range of potential strengths and wave vectors, even as it transitions between different dissipative regimes. At weak lattice potential the optical conductivity evolves as a function of 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 notably its temperature evolution can be fully understood as a consequence of umklapp hydrodynamics: i.e., 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 the transport. We confirm that in this regime the thermal diffusivity appears to be insensitive to the breaking of translations and can be explained by Planckian dissipation originating in universal microscopic chaos. A similar behavior has been found for 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. Show less
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... Show moreWe 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 limita-tion 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". Show less
Heumen, E. van; Feng, X.B.; Cassanelli, S.; Neubrand, L.; Jager, L. de; Berben, M.; ... ; Zaanen, J. 2022
Unlocking the mystery of the strange metal state has become the focal point of high-Tcresearch, not because of its importance for superconductivity, but because it appears to represent a truly... Show moreUnlocking the mystery of the strange metal state has become the focal point of high-Tcresearch, 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-Tccuprate superconductor, Bi2-xPbxSr2-yLayCuO6+delta 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 twofold: (i) a low energy Drude response with Drude width on the order of temperature and (ii) a high energy conformal tail with a doping dependent power-law exponent. While the Drude weight evolves monotonically 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. Show less
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... Show moreA 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 weak Rashba spin-orbit coupling (SOC). It is described by an emergent angular momentum J(z) = +/- 3/2 as shown by both exact diagonalization and variational Monte Carlo 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 with reducing spin-spin correlation length in the superconducting-pseudogap phase at finite doping. A brief discussion of a recent experiment of the spinpolarized ARPES will be made. Show less
In conventional superconductors, the phase transition into a zero-resistance and perfectly diamagnetic state is accompanied by a jump in the specific heat and the opening of a spectral gap(1). In... Show moreIn conventional superconductors, the phase transition into a zero-resistance and perfectly diamagnetic state is accompanied by a jump in the specific heat and the opening of a spectral gap(1). In the high-transition-temperature (high-T-c) cuprates, although the transport, magnetic and thermodynamic signatures of T-c have been known since the 1980s(2), the spectroscopic singularity associated with the transition remains unknown. Here we resolve this long-standing puzzle with a high-precision angle-resolved photoemission spectroscopy (ARPES) study on overdoped (Bi,Pb)(2)Sr2CaCu2O8+delta (Bi2212). We first probe the momentum-resolved electronic specific heat via spectroscopy and reproduce the specific heat peak at T-c, completing the missing link for a holistic description of superconductivity. Then, by studying the full momentum, energy and temperature evolution of the spectra, we reveal that this thermodynamic anomaly arises from the singular growth of in-gap spectral intensity across T-c. Furthermore, we observe that the temperature evolution of in-gap intensity is highly anisotropic in the momentum space, and the gap itself obeys both the d-wave functional form and particle-hole symmetry. These findings support the scenario that the superconducting transition is driven by phase fluctuations. They also serve as an anchor point for understanding the Fermi arc and pseudogap phenomena in underdoped cuprates. Show less
The AdS/CFT correspondence provides a unique way to study the vortex matter phases in superconductors. We solve the dynamical evolution of a superconductor in 2 thorn 1 dimensions at a finite... Show moreThe AdS/CFT correspondence provides a unique way to study the vortex matter phases in superconductors. We solve the dynamical evolution of a superconductor in 2 thorn 1 dimensions at a finite temperature subjected to a magnetic field quench in terms of a gravitational "hairy black hole" dual living in an asymptotic AdS 4 space. We exploit this to determine the nature of the equilibrium states realized at long times after the quench of this two dimensional type II superconductor in a perpendicular external uniform magnetic field B-0. This holographic superconductor exhibits the generic lower (B-c1 (T)) and upper (B-c2 (T)) critical fields. For B-0 < B-c1 (T) the magnetic field is completely expelled revealing the Meissner phase, while the superconductivity is destroyed when B-0 > B-c2 (T). Abrikosov lattices appear in the range B-c1(T) < B-0 < B-c2 (T) that realize various configurations in the form of hexagonal, square and slightly irregular square lattices pending the magnetic field strength and the influence of finite size boundaries. We show this to be consistent with the expectations of Ginzburg-Landau theory where the upper and lower critical fields are associated with the inverse squares of the coherence length and magnetic penetration depth, respectively. Show less
Ayres, J.; Berben, M.; Culo, M.; Hsu, Y.T.; Heumen, E. van; Huang, Y.; ... ; Hussey, N.E. 2021
Strange metals possess highly unconventional electrical properties, such as a linear-in-temperature resistivity(1-6), an inverse Hall angle that varies as temperature squared(7-9) and a linear-in... Show moreStrange metals possess highly unconventional electrical properties, such as a linear-in-temperature resistivity(1-6), an inverse Hall angle that varies as temperature squared(7-9) and a linear-in-field magnetoresistance(10-13). Identifying the origin of these collective anomalies has proved fundamentally challenging, even in materials such as the hole-doped cuprates that possess a simple bandstructure. The prevailing consensus is that strange metallicity in the cuprates is tied to a quantum critical point at a doping p* inside the superconducting dome(14,15). Here we study the high-field in-plane magnetoresistance of two superconducting cuprate families at doping levels beyond p*. At all dopings, the magnetoresistance exhibits quadrature scaling and becomes linear at high values of the ratio of the field and the temperature, indicating that the strange-metal regime extends well beyond p*. Moreover, the magnitude of the magnetoresistance is found to be much larger than predicted by conventional theory and is insensitive to both impurity scattering and magnetic field orientation. These observations, coupled with analysis of the zero-field and Hall resistivities, suggest that despite having a single band, the cuprate strange-metal region hosts two charge sectors, one containing coherent quasiparticles, the other scale-invariant 'Planckian' dissipators.Measurements of high-field magnetotransport in overdoped cuprates indicate that the strange-metal regime exists beyond the critical doping, and that it has both coherent and incoherent contributions. Show less
Lu, H.; Rossi, M.; Nag, A.; Osada, M.; Li, D.F.; Lee, K.; ... ; Lee, W.S. 2021
The discovery of superconductivity in infinite-layer nickelates brings us tantalizingly close to a material class that mirrors the cuprate superconductors. We measured the magnetic excitations in... Show moreThe discovery of superconductivity in infinite-layer nickelates brings us tantalizingly close to a material class that mirrors the cuprate superconductors. We measured the magnetic excitations in these nickelates using resonant inelastic x-ray scattering at the Ni L-3-edge. Undoped NdNiO2 possesses a branch of dispersive excitations with a bandwidth of approximately 200 milli-electron volts, which is reminiscent of the spin wave of strongly coupled, antiferromagnetically aligned spins on a square lattice. The substantial damping of these modes indicates the importance of coupling to rare-earth itinerant electrons. Upon doping, the spectral weight and energy decrease slightly, whereas the modes become overdamped. Our results highlight the role of Mottness in infinite-layer nickelates. Show less
Lee, W.S., Zhou, K.; Hepting, M.; Li, J.; Nag, A.; Walters, A.C.; Garcia-Fernandez, M.; ... ; Devereaux, T.P. 2021
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... Show moreWe 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. Show less
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... Show moreWe 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. Show less
