arXiv subjects

A. Khansili

Publications and source records attributed to A. Khansili.

5 recordsLinked to original sources

arXiv2026

Magnetic field as a dynamic energy scale in quantum-critical CeCoIn$_5$

Whether magnetic field enters the quantum-critical dynamics as a competing energy scale in strange metals remains an open question. Using thermal impedance spectroscopy, we simultaneously measure the electronic specific heat and spin-relaxation dynamics of CeCoIn$_5$. Both properties show scale invariance with temperature and magnetic field, where a single energy scale governs their crossover. Magnetic field thus competes directly with temperature to set the infrared cutoff, establishing it as a dynamic energy scale in the critical dynamics of this strange metal.

cond-mat.str-el↗

arXiv2025

Precursor to Quantum Criticality in Ce-Au-Al Quasicrystal Approximants

Rare-earth element containing aperiodic quasicrystals and their related periodic approximant crystals can exhibit non-trivial physical properties at low temperatures. Here, we investigate the 1/1 and 2/1 approximant crystal phases of the Ce-Au-Al system by studying the ac-susceptibility and specific heat at low temperatures and in magnetic fields up to 12 T. We find that these systems display signs of quantum criticality similar to the observations in other claimed quantum critical systems, including the related Yb-Au-Al quasicrystal. In particular, the ac-susceptibility at low temperatures shows a diverging behavior $χ\propto 1/T$ as the temperature decreases as well as cutoff-behavior in magnetic field. Notably, the field dependence of $χ$ closely resembles that of quantum critical systems. However, the ac-susceptibility both in zero and nonzero magnetic fields can be understood from the splitting of a ground state Kramers doublet of Ce$^{3+}$. The high-temperature Curie-Weiss fit yields an effective magnetic moment of approximately 2.54$μ_{\mathrm{B}}$ per Ce for both approximant systems, which is reduced to $\sim$2.0$μ_{\mathrm{B}}$ at temperatures below 10 K. The low-temperature specific heat is dominated by the Schottky anomaly originating from the splitting of the Ce$^{3+}$ Kramers doublet, resulting in an entropy of $R\ln 2$ at around 10 K.

cond-mat.str-el↗

arXiv2024

Quantum Critical Scaling of Specific Heat in a Quasicrystal

In strongly correlated systems, interactions give rise to critical fluctuations surrounding the quantum critical point (QCP) of a quantum phase transition. Quasicrystals allow the study of quantum critical phenomena in aperiodic systems with frustrated magnetic interactions. Here, we study the magnetic field and temperature scaling of the low-temperature specific heat for the quantum critical Yb-Au-Al quasicrystal. We devise a scaling function that encapsulates the limiting behaviors as well as the area where the system goes from a temperature-limited to a field-limited quantum critical region, where magnetic field acts as a cutoff for critical fluctuations. The zero-field electronic specific heat is described by a power-law divergence, ${C_{el}/T \propto T^{-0.54}}$, aligning with previously observed ac-susceptibility and specific heat measurements. The field dependence of the electronic specific heat at high magnetic fields shows a similar power-law ${C_{el}/T \propto B^{-0.50}}$. In the zero-field and low-field region, we observe two small but distinct anomalies in the specific heat, located at 0.7 K and 2.1 K.

cond-mat.str-el↗

arXiv2023

Calorimetric measurement of nuclear spin-lattice relaxation rate in metals

The quasiparticle density of states in correlated and quantum-critical metals directly probes the effect of electronic correlations on the Fermi surface. Measurements of the nuclear spin-lattice relaxation rate provide one such experimental probe of quasiparticle mass through the electronic density of states. By far the most common way of accessing the spin-lattice relaxation rate is via nuclear magnetic resonance and nuclear quadrupole resonance experiments, which require resonant excitation of nuclear spin transitions. Here we report non-resonant access to spin-lattice relaxation dynamics in AC-calorimetric measurements. The nuclear spin-lattice relaxation rate is inferred in our measurements from its effect on the frequency dispersion of the thermal response of the calorimeter-sample assembly. We use fast, lithographically-defined nanocalorimeters to access the nuclear spin-lattice relaxation times in metallic indium from 0.3~K to 7~K and in magnetic fields up to 35~T.

cond-mat.str-el↗

arXiv2022

Element-specific probe of quantum criticality in $\mathrm{CeCoIn_{5}}$

Employing the elemental sensitivity of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD), we study the valence and magnetic order in the heavy fermion superconductor CeCoIn$_5$. We probe spin population of the f-electrons in Ce and d-electrons in Co as a function of temperature (down to 0.1 K) and magnetic field (up to 6 T). From the XAS we find a pronounced contribution of Ce$^{4+}$ component at low temperature and a clear temperature dependence of the Ce valence below 5 K, suggesting enhanced valence fluctuations, an indication for the presence of a nearby quantum critical point (QCP). We observe no significant corresponding change with magnetic field. The XMCD displays a weak signal for Ce becoming clear only at 6 T. This splitting of the Kramers doublet ground state of Ce$^{3+}$ is significantly smaller than expected for independent but screened ions, indicating strong antiferromagnetic pair interactions. The unconventional character of superconductivity in CeCoIn$_5$ is evident in the extremely large specific heat step at the superconducting transition.

cond-mat.str-el↗