arXiv subjects

T. Kotte

Publications and source records attributed to T. Kotte.

6 recordsLinked to original sources

arXiv2026

High-Field Heat Capacity of Atacamite Cu$_2$Cl(OH)$_3$ for $\mathbf{H} \parallel b$ axis: From Antiferromagnetic Order to Correlated Disorder

We present the heat capacity of the frustrated sawtooth-chain compound atacamite Cu$_2$Cl(OH)$_3$ in high magnetic fields up to 35 T for $\mathbf{H} \parallel b$ axis. We clearly observe the change from antiferromagnetic long-range order, indicated by a sharp transition anomaly shifted to lower temperatures when increasing field, to a field-induced spin-liquid-like state with the absence of any transition anomaly. Here, in highest magnetic fields above 32 T a broad anomaly is present which is shifted to higher temperatures as the field is increased. The low-temperature heat capacity in the high-field region can be described well by an exponential behavior indicating a thermal activation over a spin gap. The findings are consistent with our scenario for the high-field state in atacamite for $\mathbf{H} \parallel c$ axis, where we proposed the sawtooth chains to decouple into two spin subsystems, basal and apical spin sites, leading to a partially polarized state with $M \sim M_\mathrm{sat}/2$.

cond-mat.str-el↗

arXiv2026

Sb-5$p$-mediated antiparallel Nd-Fe coupling in Nd$_3$Fe$_3$Sb$_7$

We uncover the microscopic mechanism underlying the antiparallel Nd-Fe coupling in the intermetallic 4$f$-3$d$-5$p$ compound Nd$_3$Fe$_3$Sb$_7$ by means of high-field x-ray magnetic circular dichroism (XMCD) spectroscopy, complemented by magnetization measurements and density-functional-theory (DFT) calculations. This coupling is unexpected for intermetallics composed of light rare-earth and transition-metal elements. Sb $M_{4,5}$-edge XMCD measurements indicate a clear spin polarization of Sb 5$p$ states antiparallel to the Fe 3$d$ moments. DFT calculations reveal the site-dependent character of the Sb moments and, together with the Fe-Sb antiparallel alignment seen by XMCD, identify a Fe 3$d$-Sb 5$p$-Nd 5$d$ hybridization pathway for the antiparallel Nd-Fe coupling. Pulsed-field XMCD reveals a field-induced spin reorientation through the evolution of the $c$-axis projections of the Nd and Fe moments. Nd$_3$Fe$_3$Sb$_7$, thus, provides a platform for exploring antiparallel rare-earth-transition-metal ($R$-$T$) coupling mediated by transition-metal 3$d$-ligand $p$-rare-earth 5$d$ hybridization in light-$R$-$T$ intermetallics with $p$-elements.

cond-mat.mtrl-sci↗

arXiv2025

Atacamite Cu$_2$Cl(OH)$_3$ in High Magnetic Fields: Quantum Criticality and Dimensional Reduction of a Sawtooth-Chain Compound

We report an extensive high-field study of atacamite Cu$_2$Cl(OH)$_3$, a material realization of quantum sawtooth chains with weak interchain couplings, in continuous and pulsed magnetic fields up to 58 T. In particular, we have mapped the entropy landscape for fields as high as 35 T and have identified a field-induced quantum critical point at 21.9(1) T for $\mathbf{H} \parallel c$ axis. The quantum critical point separates field regions with and without magnetic order, evidenced by our thermodynamic study and $^1$H nuclear magnetic resonance spectroscopy, but lies far below full saturation of the magnetization. Corroborated by numerical results using density-matrix renormalization group (DMRG) calculations, we find this behavior associated with a dimensional reduction of the spin system: the sawtooth chain effectively decouples into an antiferromagnetic spin-$1/2$ chain (backbone of the sawtooth chain) in the presence of an exchange field produced by the remaining field-polarized spins.

cond-mat.str-el↗

arXiv2025

Rotational magnetoelastic interactions in the Dzyaloshinskii-Moriya magnet Ba$_2$CuGe$_2$O$_7$

We report the magnetoelastic properties of a Ba$_2$CuGe$_2$O$_7$ single crystal at low temperatures under a magnetic field applied along the crystallographic [001] axis. Our results extend to low temperature the $H-T$ phase diagram determined for this compound by neutron scattering. Furthermore, we observe that specific elastic modes are better sensitive to the various magnetic transitions. In particular, we observe an unusual coupling between the in-plane transverse acoustic mode and the cycloidal order at low field, which suggests a novel spin-strain mechanism originating from Dzyaloshinskii-Moriya interaction in this compound.

cond-mat.str-el↗

arXiv2024

Origin of the non-Fermi-liquid behavior in CeRh2As2

Unconventional superconductivity in heavy-fermion systems appears often near magnetic quantum critical points (QCPs). This seems to be the case also for CeRh2As2 (Tc $\approx$ 0.31 K). CeRh2As2 shows two superconducting (SC) phases, SC1 and SC2, for a magnetic field along the c axis of the tetragonal unit cell, but only the SC1 phase is observed for a field along the basal plane. Furthermore, another ordered state (phase-I) is observed below T0 $\approx$ 0.48 K whose nature is still unclear: Thermodynamic and magnetic measurements pointed to a non magnetic multipolar state, but recent $μ$SR and NQR/NMR experiments have clearly detected antiferromagnetic (AFM) order below T0 . Also, quasi-two-dimensional AFM fluctuations were observed in NMR and neutron-scattering experiments above T0. The proximity of a QCP is indicated by non-Fermi-liquid (NFL) behavior observed above the ordered states in both specific heat $C(T)/T \propto T^{-0.6}$ and resistivity $ρ(T) \propto T^{0.5}$. These T-dependencies are not compatible with any generic AFM QCP. Because of the strong magnetic-field anisotropy of both the SC phase and phase I, it is possible to study a field-induced SC QCP as well a phase-I QCP by varying the angle $α$ between the field and the c axis. Thus, by examining the behavior of the electronic specific-heat coefficient C(T)/T across these QCPs, we can determine which phase is associated with the NFL behavior. Here, we present low-temperature specific-heat measurements taken in a magnetic field as high as 21 T applied at several angles $α$. We observe that the NFL behavior does very weakly depend on the field and on the angle $α$, a result that is at odd with that observations in standard magnetic QCPs. This suggests a nonmagnetic origin of the quantum critical fluctuations.

cond-mat.str-el↗

arXiv2024

Giant quantum oscillations in thermal transport in low-density metals via electron absorption of phonons

Oscillations of conductance observed in strong magnetic fields are a striking manifestation of the quantum dynamics of charge carriers in solids. The large charge carrier density in typical metals sets the scale of oscillations in both electrical and thermal conductivity, which characterize the Fermi surface. In semimetals, thermal transport at low-charge carrier density is expected to be phonon dominated, yet several experiments observe giant quantum oscillations in thermal transport. This raises the question of whether there is an overarching mechanism leading to sizable oscillations that survives in phonon-dominated semimetals. In this work, we show that such a mechanism exists. It relies on the peculiar phase-space allowed for phonon scattering by electrons when only a few Landau levels are filled. Our measurements on the Dirac semimetal ZrTe5 support this counter-intuitive mechanism through observation of pronounced thermal quantum oscillations, since they occur in similar magnitude and phase in directions parallel and transverse to the magnetic field. Our phase-space argument applies to all low-density semimetals, topological or not, including graphene and bismuth. Our work illustrates that phonon absorption can be leveraged to reveal degrees of freedom through their imprint on longitudinal thermal transport.

cond-mat.str-el↗