arXiv subjects

A. Bangura

Publications and source records attributed to A. Bangura.

7 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↗

arXiv2023

Wide Range Thin-FIlm Ceramic Metal-Alloy Thermometers with Low Magnetoresistance

Many thermal measurements in high magnetic fields require thermometers that are sensitive over a wide temperature range, are low mass, have a rapid thermal response, and have a minimal, easily correctable magnetoresistance. Here we report the development of a new granular-metal oxide ceramic composite (cermet) for this purpose formed by co-sputtering of the metallic alloy nichrome Ni$_{0.8}$Cr$_{0.2}$ and the insulator silcon dioxide SiO$_2$. The resulting thin films are sensitive enough to be used from room temperature down to below 100 mK in magnetic fields up to at least 35 tesla.

cond-mat.mtrl-sci↗

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↗

arXiv2005

Recent high-magnetic-field studies of unusual groundstates in quasi-two-dimensional crystalline organic metals and superconductors

After a brief introduction to crystalline organic superconductors and metals, we shall describe two recently-observed exotic phases that occur only in high magnetic fields. The first involves measurements of the non-linear electrical resistance of single crystals of the charge-density-wave (CDW) system (Per)$_2$Au(mnt)$_2$ in static magnetic fields of up to 45 T and temperatures as low as 25 mK. The presence of a fully gapped CDW state with typical CDW electrodynamics at fields higher that the Pauli paramagnetic limit of 34 T suggests the existence of a modulated CDW phase analogous to the Fulde-Ferrell-Larkin-Ovchinnikov state. Secondly, measurements of the Hall potential of single crystals of $α$-(BEDT-TTF)$_2$KHg(SCN)$_4$, made using a variant of the Corbino geometry in quasistatic magnetic fields, show persistent current effects that are similar to those observed in conventional superconductors. The longevity of the currents, large Hall angle, flux quantization and confinement of the reactive component of the Hall potential to the edge of the sample are all consistent with the realization of a new state of matter in CDW systems with significant orbital quantization effects in strong magnetic fields.

cond-mat.supr-con↗

arXiv2004

Landau quantization effects in the charge-density-wave system (Per)$_2M$(mnt)$_2$ (where $M=$Au and Pt)

A finite transfer integral $t_a$ orthogonal to the conducting chains of a highly one-dimensional metal gives rise to empty and filled bands that simulate an indirect-gap semiconductor upon formation of a commensurate charge-density-wave (CDW). In contrast to semiconductors such as Ge and Si with bandgaps $\sim 1$ eV, the CDW system possesses an indirect gap with a greatly reduced energy scale, enabling moderate laboratory magnetic fields to have a major effect. The consequent variation of the thermodynamic gap with magnetic field due to Zeeman splitting and Landau quantization enables the electronic bandstructure parameters (transfer integrals, Fermi velocity) to be determined accurately. These parameters reveal the orbital quantization limit to be reached at $\sim 20$ T in (Per)$_2M$(mnt)$_2$ salts, making them highly unlikely candidates for a recently-proposed cascade of field-induced charge-density wave states.

cond-mat.str-el↗

arXiv2004

Suppression of the $γ-α$ structural phase transition in $Ce_{0.8} La_{0.1} Th_{0.1}$ by large magnetic fields

The $γ-α$ transition in Ce$_{0.8}$La$_{0.1}$Th$_{0.1}$ is measured as a function of applied magnetic field using both resistivity and magnetization. The $γ- α$ transition temperature decreases with increasing magnetic field, reaching zero temperature at around 56 T. The magnetic-field dependence of the transition temperature may be fitted using a model that invokes the field and temperature dependence of the entropy of the $4f$-electron moments of the $γ$ phase, suggesting that the volume collapse in Ce and its alloys is primarily driven by entropic considerations.

cond-mat.str-el↗

arXiv2003

A new quantum fluid at high magnetic fields in the marginal charge-density-wave system $α$-(BEDT-TTF)$_2M$Hg(SCN)$_4$ (where $M=$~K and Rb)

Single crystals of the organic charge-transfer salts $α$-(BEDT-TTF)$_2M$Hg(SCN)$_4$ have been studied using Hall-potential measurements ($M=$K) and magnetization experiments ($M$ = K, Rb). The data show that two types of screening currents occur within the high-field, low-temperature CDW$_x$ phases of these salts in response to time-dependent magnetic fields. The first, which gives rise to the induced Hall potential, is a free current (${\bf j}_{\rm free}$), present at the surface of the sample. The time constant for the decay of these currents is much longer than that expected from the sample resistivity. The second component of the current appears to be magnetic (${\bf j}_{\rm mag}$), in that it is a microscopic, quasi-orbital effect; it is evenly distributed within the bulk of the sample upon saturation. To explain these data, we propose a simple model invoking a new type of quantum fluid comprising a CDW coexisting with a two-dimensional Fermi-surface pocket which describes the two types of current. The model and data are able to account for the body of previous experimental data which had generated apparently contradictory interpretations in terms of the quantum Hall effect or superconductivity.

cond-mat.str-el↗