arXiv subjects

T. Cichorek

Publications and source records attributed to T. Cichorek.

15 recordsLinked to original sources

arXiv2025

Nodeless Superconducting State in the Presence of Zero-Field Staggered Magnetization in CeRh$_{2}$As$_{2}$

The tetragonal heavy-fermion superconductor CeRh$_{2}$As$_{2}$ with a critical temperature $T_c$ $\approx$ 0.34 K exhibits an intriguing magnetic field-induced transition between likely distinct superconducting states. In zero field, an even-parity state emerges within another ordered phase of unknown origin with $T_0$ $\approx$ 0.54 K. Here, we investigated the spin-singlet state of CeRh$_{2}$As$_{2}$ at temperatures down to $\approx$ 0.02$T_c$ by means of local magnetization measurements performed using micro-Hall probe magnetometry. We determined the temperature dependencies of the lower critical field for both in-plane and out-of-plane field directions, and demonstrated their consistency with predominantly fully gapped superconductivity. In the magnetization measured along the $a$ axis, we found a clear increase below $T_0$, while no similar anomaly was observed along the $c$ axis. Our results place important constraints on the spin-singlet order parameter in CeRh$_{2}$As$_{2}$ and highlight an important role of static magnetic moments in the nature of $T_0$ phase.

cond-mat.supr-con↗

arXiv2023

Magnetostriction of metals with small Fermi-surface pockets: Case of the topologically trivial semimetal LuAs

We develop a theory of the magnetostriction for metals with small charge-carrier pockets of their Fermi surfaces. As an example, we consider LuAs that has a cubic crystal structure. The theory quite well describes the known experimental data on the magnetostriction of this metal. The obtained results also clearly demonstrate that the dilatometry can be used for detecting tiny Fermi-surface pockets that are not discerned by traditional methods based on investigations of the Shubnikov--de Haas and de Haas--van Alphen effects.

cond-mat.mtrl-sci↗

arXiv2023

Temperature dependence of the lower critical field of the noncentrosymmetric superconductor $α$-BiPd

Temperature variation of the lower critical field in the noncentrosymmetric superconductor $α$-BiPd was probed by local magnetization measurements using Hall micromagnetometry, performed down to 0.3 K in a magnetic field applied along the crystallographic $b$ axis. Below a critical temperature $T_c \simeq$ 3.8 K, a conventional $H_{c1}(T)$ dependence was found, typical for a single-band $s$-wave BCS superconductor. The obtained data imply an absence of spin-triplet component in the superconducting wavefunction and marginal multiband effects in this material, which contradicts some literature reports.

cond-mat.supr-con↗

arXiv2022

Multigap Superconductivity in the Filled-Skutterudite Compound LaRu$_4$As$_{12}$ probed by muon spin rotation

Muon spin rotation ($μ$SR) and inelastic X-ray scattering (IXS) were used to investigate the superconducting properties of the filled-skutterudite compound LaRu$_{4}$As$_{12}$. A two-gap isotropic ($s+s$)-wave model can explain the temperature dependence of the superfluid density. Zero field $μ$SR measurements confirm that the time-reversal symmetry does not break upon entering the superconducting state. The measurements of lattice dynamics at 2, 20 and 300 K revealed temperature dependencies of the phonon modes that do not follow strictly a hardening of phonon frequencies upon cooling as expected within the quasi-harmonic picture. The 20~K data rather mark a turning point for the majority of the phonon frequencies. Indeed a hardening is observed approaching 20~K from above, while for a few branches a weak softening is visible upon further cooling to 2~K. The observed dispersion relations of phonon modes throughout the Brillouin zone matches with the DFT prediction quite closely. Our results point out that cubic LaRu$_{4}$As$_{12}$ is a good reference material for studying multiband superconductivity, including those with lower crystallographic symmetries such as iron arsenide-based superconductors.

cond-mat.supr-con↗

arXiv2022

Detection of relativistic fermions in Weyl semimetal TaAs by magnetostriction measurements

Thus far, a detection of the Dirac or Weyl fermions in topological semimetals remains often elusive, since in these materials conventional charge carriers exist as well. Here, measuring a field-induced length change of the prototype Weyl semimetal TaAs at low temperatures, we find that its $c$-axis magnetostriction amounts to relatively large values whereas the $a$-axis magnetostriction exhibits strong variations with changing the orientation of the applied magnetic field. It is discovered that at magnetic fields above the ultra-quantum limit, the magnetostriction of TaAs contains a linear-in-field term, which, as we show, is a hallmark of the Weyl fermions in a material. Developing a theory for the magnetostriction of noncentrosymmetric topological semimetals and applying it to TaAs, we additionally find several parameters characterizing the interaction between the relativistic fermions and elastic degrees of freedom in this semimetal. Our study shows how dilatometry can be used to unveil Weyl fermions in candidate topological semimetals.

cond-mat.mes-hall↗

arXiv2016

Two-channel Kondo physics due to As vacancies in the layered compound ZrAs1.58Se0.39

We address the origin of the magnetic-field independent -|A| T^{1/2} term observed in the low-temperature resistivity of several As-based metallic systems of the PbFCl structure type. For the layered compound ZrAs_{1.58}Se_{0.39}, we show that vacancies in the square nets of As give rise to the low-temperature transport anomaly over a wide temperature regime of almost two decades in temperature. This low-temperature behavior is in line with the non-magnetic version of the two-channel Kondo effect, whose origin we ascribe to a dynamic Jahn-Teller effect operating at the vacancy-carrying As layer with a C_4 symmetry. The pair-breaking nature of the dynamical defects in the square nets of As explains the low superconducting transition temperature T_{\rm{c}}\approx 0.14 K of ZrAs_{1.58}Se_{0.39}, as compared to the free-of-vacancies homologue ZrP_{1.54}S_{0.46} (T_{\rm{c}}\approx 3.7 K). Our findings should be relevant to a wide class of metals with disordered pnictogen layers.

cond-mat.str-el↗

arXiv2008

The filled skutterudite CeOs$_{4}$As$_{12}$: a hybridization gap semiconductor

X-ray diffraction, electrical resistivity, magnetization, specific heat, and thermoelectric power measurements are presented for single crystals of the new filled skutterudite compound {\CeOsAs}, which reveal phenomena that are associated with f - electron - conduction electron hybridization. Valence fluctuations or Kondo behavior dominates the physics down to $T$ $\sim$ 135 K. The correlated electron behavior is manifested at low temperatures as a hybridization gap insulating state. The small energy gap $Δ$$_1$/k$_B$ $\sim$ 73 K, taken from fits to electrical resistivity data, correlates with the evolution of a weakly magnetic or nonmagnetic ground state, which is evident in the magnetization data below a coherence temperature $T$$_{coh}$ $\sim$ 45 K. Additionally, the low temperature electronic specific heat coefficient is small, $γ$ $\sim$ 19 mJ/mol K$^2$. Some results for the nonmagnetic analogue compound {\LaOsAs} are also presented for comparison purposes.

cond-mat.str-el↗

arXiv2007

Non-Fermi liquid behavior in a fluctuating valence system, the filled skutterudite compound CeRu_{4}As_{12}

Electrical resistivity $ρ$, specific heat C, and magnetic susceptibility $χ$ measurements made on the filled skutterudite CeRu_4As_{12} reveal non-Fermi liquid (NFL) T - dependences at low T, i.e., $ρ$(T) $\sim$ T^{1.4} and weak power law or logarithmic divergences in C(T)/T and $χ$(T). Measurements also show that the T - dependence of the thermoelectric power S(T) deviates from that seen in other Ce systems. The NFL behavior appears to be associated with fluctuations of the Ce valence between 3^+ and 4^+ rather than a typical Kondo lattice scenario that would be appropriate for an integral Ce valence of 3^+.

cond-mat.str-el↗

arXiv2005

Crystallographic disorder and electron scattering on structural two-level systems in ZrAs1.4Se0.5

Single crystals of ZrAs1.4Se0.5 (PbFCl type structure) were grown by chemical vapour transport. While their thermodynamic and transport properties are typical for ordinary metals, the electrical resistivity exhibits a shallow minimum at low temperatures. Application of strong magnetic fields does not influence this anomaly. The minimum of the resistivity in ZrAs1.4Se0.5 apparently originates from interaction between the conduction electrons and structural two-level systems. Significant disorder in the As-Se substructure is inferred from X-ray diffraction and electron microprobe studies.

cond-mat.str-el↗

arXiv2005

Two-Cannel Kondo Effect in Glass-Like ThAsSe

We present low-temperature heat and charge transport as well as caloric properties of a ThAsSe single crystal. An extra -AT1/2 term in the electrical resistivity, independent of magnetic fields as high as 14 T, provides evidence for an unusual scattering of conduction electrons. Additionally, both the thermal conductivity and specific heat show a glass-type temperature dependence which signifies the presence of tunneling states. These observations apparently point to an experimantal realization of a two-channel Kondo effect derived from structural two-level systems.

cond-mat.str-el↗

arXiv2005

Unusual magnetic properties of the low-dimensional quantum magnet Na2V3O7

We report the results of low-temperature measurements of the specific heat Cp(T), ac susceptibility chi(T) and 23Na nuclear magnetic resonance NMR of Na2V3O7. At liquid He temperatures Cp(T)/T exhibits broad field-dependent maxima, which shift to higher temperatures upon increasing the applied magnetic field H. Below 1.5 K the ac magnetic susceptibility chi(T) follows a Curie-Weiss law and exhibits a cusp at 0.086 mK which indicates a phase transition at very low temperatures. These results support the previous conjecture that Na2V3O7 is close to a quantum critical point (QCP) at mu_{0}H = 0 T. The entire data set, including results of measurements of the NMR spin-lattice relaxation 1/T1(T), reveals a complex magnetic behavior at low temperatures. We argue that it is due to a distribution of singlet-triplet energy gaps of dimerized V moments. The dimerization process evolves over a rather broad temperature range around and below 100 K. At the lowest temperatures the magnetic properties are dominated by the response of only a minor fraction of the V moments.

cond-mat.str-el↗

arXiv2004

Pronounced enhancement of the lower critical field and critical current deep in the superconducting state of PrOs$_4$Sb$_{12}$

We have observed an unexpected enhancement of the lower critical field $H_{c1}(T)$ and the critical current $I_{c}(T)$ deep in the superconducting state below $T \approx 0.6$ K ($T/T_{c} \approx 0.3$) in the filled skutterudite heavy fermion superconductor PrOs$_4$Sb$_{12}$. From a comparison of the behavior of $H_{c1}(T)$ with that of the heavy fermion superconductors U$_{1-x}$Th$_x$Be$_{13}$ and UPt$_3$, we speculate that the enhancement of $H_{c1}(T)$ and $I_{c}(T)$ in PrOs$_4$Sb$_{12}$ reflects a transition into another superconducting phase that occurs below $T/T_{c} \approx 0.3$. An examination of the literature reveals unexplained anomalies in other physical properties of PrOs$_4$Sb$_{12}$ near $T/T_{c} \approx 0.3$ that correlate with the features we have observed in $H_{c1}(T)$ and $I_{c}(T)$.

cond-mat.supr-con↗

arXiv2003

Divergence of the Grueneisen Ratio at Quantum Critical Points in Heavy Fermion Metals

We present low-temperature volume thermal expansion, $β$, and specific heat, $C$, measurements on high-quality single crystals of CeNi2Ge2 and YbRh2(Si$_{0.95}$Ge$_{0.05}$)$_2$ which are located very near to quantum critical points. For both systems, $β$ shows a more singular temperature dependence than $C$, and thus the Grueneisen ratio ${Γ\propto β/C}$ diverges as T --> 0. For CeNi2Ge2, our results are in accordance with the spin-density wave (SDW) scenario for three-dimensional critical spin-fluctuations. By contrast, the observed singularity in YbRh2$(Si$_{0.95}$Ge$_{0.05}$)$_2$ cannot be explained by the itinerant SDW theory but is qualitatively consistent with a locally quantum critical picture.

cond-mat.str-el↗

arXiv2001

Specific heat and disorder in the mixed state of non-magnetic borocarbides

The temperature and magnetic field dependence of the specific heat cp(T,H) in the superconducting mixed state as well as the upper critical field Hc2(T) have been measured for polycrystalline Y_xLu_{1-x}Ni_2B_2C and Y(Ni_{1-y}Pt_y)_2B_2C samples. The linear-in-T electronic specific heat contribution gamma(H)T exhibits significant deviations from the usual linear-in-H law for all x and y the transition metal site (T) resulting in a disorder dependent negative curvature of gamma(H). The deviations from that linear behaviour of our unsubstituted samples are the largest reported so far for any superconductor. The H_c2(T) data point to the quasi-clean limit for (Y,Lu)-substitutions and to a transition to the quasi-dirty limit for (Ni,Pt)-substitutions. The gamma(H) dependence is discussed in the unitary d-wave as well as in the quasi-clean s-wave limits. From a consideration of gamma(H) data only, d-wave pairing cannot be ruled out.

cond-mat.supr-con↗

arXiv2000

Specific heat of (Y,Lu)Ni2B2C in the mixed state

The temperature and magnetic field dependences of the electronic specific heat in the superconducting mixed state as well as the upper critical field have been measured on a (Y,Lu)Ni2B2C series to study the influence of disorder. The electronic specific heat in the vortex state shows deviations from the usual gamma(H) proportional to H-law for conventional superconductors for all samples resulting in a disorder dependent negative curvature of gamma proportional to H sup(1-beta). For samples with disorder at the R site beta and the positive curvature exponent alpha of H sub(c2) are reduced but alpha, beta remain always positive, as distinct from much stronger disorder due to Pt substions at the Ni site where alpha, beta rapidly tend to 0. Alpha shows a minimum at equal Y and Lu concentration. H sub(c2)(00, T sub(c), the curvatures of H sub(c2) and gamma(h), as well as the normal state Sommerfeld constant gamma sub(N) are reduced similarly.

cond-mat↗