24 research outputs found
Strange Half Metals and Mott Insulators in SYK Models
We study a dual flavor fermion model where each of the flavors form a
Sachdev-Ye-Kitaev (SYK) system with arbitrary and possibly distinct -body
interactions. The crucial new element is an arbitrary all-to-all -body
interaction between the two flavors. At high temperatures the model shows a
strange metal phase where both flavors are gapless, similar to the usual single
flavor SYK model. Upon reducing temperature, the coupled system undergoes phase
transitions to previously unseen phases - first, a strange half metal (SHM)
phase where one flavor remains a strange metal while the other is gapped, and,
second, a Mott insulating phase where both flavors are gapped. At a fixed low
temperature we obtain transitions between these phases by tuning the relative
fraction of sites for each flavor. We discuss the physics of these phases and
the nature of transitions between them. This work provides an example of an
instability of the strange metal with potential to provide new routes to study
strongly correlated systems through the rich physics contained in SYK like
models.Comment: 7 pages, 3 figure
Nematic phases and elastoresistivity from a multiorbital strange metal
We propose and study a two-orbital lattice extension of the Sachdev-Ye-Kitaev
model in the large- limit. The phase diagram of this model features a high
temperature isotropic strange metal which undergoes a first-order thermal
transition into a nematic insulator or a continuous thermal transition into
nematic metal phase, separated by a tunable tricritical point. These phases
arise from spontaneous partial orbital polarization of the multiorbital
non-Fermi liquid. We explore the spectral and transport properties of this
model, including the d.c. elastoresistivity, which exhibits a peak near the
nematic transition, as well as the nonzero frequency elastoconductivity. Our
work offers a useful perspective on nematic phases and transport in correlated
multiorbital systems.Comment: 7 pages, 4 figure
Probing magnetic anisotropy and spin-reorientation transition in 3D antiferromagnet, HoDyFeOPt using spin Hall magnetoresistance
Orthoferrites (FeO) containing rare-earth () elements are 3D
antiferromagnets (AFM) that exhibit characteristic weak ferromagnetism
originating due to slight canting of the spin moments and display a rich
variety of spin reorientation transitions in the magnetic field
()-temperature () parameter space. We present spin Hall magnetoresistance
(SMR) studies on a -plate (-plane) of crystalline
HoDyFeOPt (HDFOPt) hybrid at various in the
range, 11 to 300 K. In the room temperature phase,
the switching between two degenerate domains, and
occurs at fields above a critical value, Oe. Under , the angular dependence of SMR
(-scan) in the phase yielded a highly skewed
curve with a sharp change (sign-reversal) along with a rotational hysteresis
around -axis. This hysteresis decreases with an increase in . Notably, at
, the -scan measurements on the single domain,
exhibited an anomalous sinusoidal signal of
periodicity 360 deg. Low- SMR curves ( = 2.4 kOe), showed a systematic
narrowing of the hysteresis (down to 150 K) and a gradual reduction in the
skewness (150 to 52 K), suggesting weakening of the anisotropy possibly due to
the -evolution of Fe- exchange coupling. Below 25 K, the SMR modulation
showed an abrupt change around the -axis, marking the presence of
phase. We have employed a simple Hamiltonian and
computed SMR to examine the observed skewed SMR modulation. In summary, SMR is
found to be an effective tool to probe magnetic anisotropy as well as a spin
reorientation in HDFO. Our spin-transport study highlights the potential of
HDFO for future AFM spintronic devices.Comment: 12 pages, 7 figure
Probing the dynamics of an optically trapped particle by phase sensitive back focal plane interferometry
The dynamics of an optically trapped particle are often determined by
measuring intensity shifts of the back-scattered light from the particle using
position sensitive detectors. We present a technique which measures the phase
of the back-scattered light using balanced detection in an external Mach-Zender
interferometer scheme where we separate out and beat the scattered light from
the bead and that from the top surface of our trapping chamber. The technique
has improved axial motion resolution over intensity-based detection, and can
also be used to measure lateral motion of the trapped particle. In addition, we
are able to track the Brownian motion of trapped 1 and 3 m diameter beads
from the phase jitter and show that, similar to intensity-based measurements,
phase measurements can also be used to simultaneously determine displacements
of the trapped bead as well as the spring constant of the trap. For lateral
displacements, we have matched our experimental results with a simulation of
the overall phase contour of the back-scattered light for lateral displacements
by using plane wave decomposition in conjunction with Mie scattering theory.
The position resolution is limited by path drifts of the interferometer which
we have presently reduced to obtain a displacement resolution of around 2 nm
for 1.1 m diameter probes by locking the interferometer to a frequency
stabilized diode laser.Comment: 10 pages, 7 figure
Cooling a Band Insulator with a Metal: Fermionic Superfluid in a Dimerized Holographic Lattice
A cold atomic realization of a quantum correlated state of many fermions on a lattice, eg. superfluid, has eluded experimental realization due to the entropy problem. Here we propose a route to realize such a state using holographic lattice and confining potentials. The potentials are designed to produces aband insulating state (low heat capacity) at the trap center, and a metallic state (high heat capacity) at the periphery. The metal ``cools'' the central band insulator by extracting out the excess entropy. The central band insulator can be turned into a superfluid by tuning an attractive interaction between the fermions. Crucially, the holographic lattice allows the emergent superfluid to have a high transition temperature - even twice that of the effective trap temperature. The scheme provides a promising route to a laboratory realization of a fermionic lattice superfluid, even while being adaptable to simulate other many body states
Quench, thermalization and residual entropy across a non-Fermi liquid to Fermi liquid transition
We study the thermalization, after sudden and slow quenches, of an interacting model having a quantum phase transition from a Sachdev-Ye-Kitaev (SYK) non-Fermi liquid (NFL) to a Fermi liquid (FL). The model has SYK fermions coupled to non-interacting lead fermions and can be realized in a graphene flake connected to external leads. After a sudden quench to the NFL, a thermal state is reached rapidly via collapse-revival oscillations of the quasiparticle residue of the lead fermions. In contrast, the quench to the FL, across the NFL-FL transition, leads to multiple prethermal regimes and much slower thermalization. In the slow quench performed over a time , we find that the excitation energy generated has a remarkable intermediate- non-analytic power-law dependence, with , which seemingly masks the dynamical manifestation of the initial residual entropy of the SYK fermions. The power-law scaling is expected to eventually break down for , signaling a violation of adiabaticity, due to the residual entropy present in the SYK fermions
Higher-dimensional Sachdev-Ye-Kitaev non-Fermi liquids at Lifshitz transitions
We address the key open problem of a higher-dimensional generalization of the Sachdev-Ye-Kitaev (SYK) model. We construct a model on a lattice of SYK dots with nonrandom intersite hopping. The crucial feature of the resulting band dispersion is the presence of a Lifshitz point where two bands touch with a tunable power-law divergent density of states (DOS). For a certain regime of the power-law exponent, we obtain a class of interaction-dominated non-Fermi-liquid (NFL) states, which exhibits exciting features such as a zero-temperature scaling symmetry, an emergent (approximate) time reparameterization invariance, a power-law entropy-temperature relationship, and a fermion dimension that depends continuously on the DOS exponent. Notably, we further demonstrate that these NFL states are fast scramblers with a Lyapunov exponent lambda(L) proportional to T, although they do not saturate the upper bound of chaos, rendering them truly unique