arXiv subjects

Priscila F. S. Rosa

Publications and source records attributed to Priscila F. S. Rosa.

At least 37 records · Page 2Linked to original sources

arXiv2023

Sudden adiabaticity entering field-induced state in UTe2

There has been a recent surge of interest in UTe$_2$ due to its unconventional magnetic field (H) reinforced spin-triplet superconducting phases persisting at fields far above the simple Pauli limit for H $\parallel$ [010]. Magnetic fields in excess of 35 T then induce a field-polarized magnetic state via a first-order-like phase transition. More controversially, for field orientations close to H $\parallel$ [011] and above 40 T, electrical resistivity measurements suggest that a further superconducting state may exist. However, no Meissner effect or thermodynamic evidence exists to date for this phase making it difficult to exclude a simple low-resistance metallic state. In this paper, we describe a study using thermal, electrical, and magnetic probes in magnetic fields of up to 55 T applied between the [010] ($b$) and [001] ($c$) directions. Our MHz conductivity data reveal the field-induced state of low or vanishing electrical resistance; simultaneous magnetocaloric effect measurements (i.e. changes in sample temperature due to changing magnetic field), show the first definitive evidence for adiabaticity and thermal behavior characteristic of bulk field-induced superconductivity.

cond-mat.supr-con↗

arXiv2023

The Reverse Quantum Limit: Implications for Unconventional Quantum Oscillations in YbB$_{12}$

Beyond the quantum limit, many-body effects are expected to induce unusual electronic phase transitions. Materials possessing metallic ground states with strong interactions between localized and itinerant electronic states are natural candidates for the realization of such quantum phases. However, the electronic correlations responsible for increasing the likelihood of novel phases simultaneously place the quantum limit beyond the reach of laboratory magnets. Here we propose these difficulties can be surmounted in materials with strong correlations and insulating ground states. Strong correlations in insulators and high magnetic fields conspire to fill Landau levels in the reverse order compared to conventional metals, such that the lowest Landau level is the first observed. Consequently, the quantum limit in strongly correlated insulators is reached in reverse and at fields accessible in laboratories. Quantum oscillations measured at high fields in YbB12 are shown to have features consistent with the reverse quantum limit. These include how quantum oscillations move in lock step with the angular evolution of the insulator-metal transition and the field dependence of the quantum oscillation frequency. We argue that close to the insulator-metal transition, the insulating state should be viewed through the lens of a magnetic field-induced electronic instability affecting the lowest Landau level states in the quantum limit.

cond-mat.str-el↗

arXiv2023

Nodeless superconductivity in the noncentrosymmetric ThIrSi compound

The ThIrSi superconductor, with $T_c = 6.5$ K, is expected to show unusual features in view of its noncentrosymmetric structure and the presence of heavy elements featuring a sizable spin-orbit coupling. Here, we report a comprehensive study of its electronic properties by means of local-probe techniques: muon-spin rotation and relaxation ({\textmu}SR) and nuclear magnetic resonance (NMR). Both the superfluid density $ρ_\mathrm{sc}(T)$ (determined via transverse-field {\textmu}SR) and the spin-lattice relaxation rate $T_1^{-1}(T)$ (determined via NMR) suggest a nodeless superconductivity. Furthermore, the absence of spontaneous magnetic fields below $T_c$, as evinced from zero-field {\textmu}SR measurements, indicates a preserved time-reversal symmetry in the superconducting state of ThIrSi. Temperature-dependent upper critical fields as well as field-dependent superconducting muon-spin relaxations suggest the presence of multiple superconducting gaps in ThIrSi.

cond-mat.supr-con↗

arXiv2023

Magnetic and electronic properties of Eu$_5$In$_2$Sb$_6$

The intermetallic compound Eu$_5$In$_2$Sb$_6$, an antiferromagnetic material with nonsymmorphic crystalline structure, is investigated by magnetic, electronic transport and specific heat measurements. Being a Zintl phase, insulating behavior is expected. Our thermodynamic and magnetotransport measurements along different crystallographic directions strongly indicate polaron formation well above the magnetic ordering temperatures. Pronounced anisotropies of the magnetic and transport properties even above the magnetic ordering temperature are observed despite the Eu$^{2+}$ configuration which testify to complex and competing magnetic interactions between these ions and give rise to intricate phase diagrams discussed in detail. Our results provide a comprehensive framework for further detailed study of this multifaceted compound with possible nontrivial topology.

cond-mat.mtrl-sci↗

arXiv2022

Interwoven atypical quantum states in CeLiBi$_2$

We report the discovery of CeLiBi$_2$, the first example of a material in the tetragonal Ce$TX_2$ ($T$ = transition metal; $X$ = pnictogen) family wherein an alkali cation replaces the typical transition metal. Magnetic susceptibility and neutron powder diffraction measurements are consistent with a crystal-field $Γ_6$ ground state Kramers doublet that orders antiferromagnetically below $T_N = 3.4$ K with an incommensurate propagation wave vector ${\bf{k}} = (0, 0.0724(4), 0.5)$ that generates a nanometric modulation of the magnetic structure. The best model of the ordered state is an elliptical cycloid with Ce moments primarily residing in the $ab$ plane. This is highly unusual, as all other $Γ_6$ Ce$TX_2$ members order ferromagnetically. Further, we observe an atypical hard-axis metamagnetic transition at $2$ T in magnetostriction, magnetization, and resistivity measurements. CeLiBi$_2$ is a rare example of a highly conductive material with dominant skew scattering leading to a large anomalous Hall effect. Quantum oscillations with five frequencies arise in magnetostriction and magnetic susceptibility data to $T = 30$ K and $μ_0H = 55$ T, which indicate small Fermi pockets of light carriers with effective masses as low as 0.07$m_e$. Density functional theory calculations indicate that square-net Dirac-like Bi$-p$ bands are responsible for these ultralight carriers. Together, our results show that CeLiBi$_2$ enables multiple atypical magnetic and electronic properties in a single clean material.

cond-mat.str-el↗

arXiv2022

Microscopic imaging homogeneous and single phase superfluid density in UTe$_2$

The spin-triplet superconductor UTe$_2$ shows spontaneous time-reversal symmetry breaking and multiple superconducting phases in some crystals, implying chiral superconductivity. Here we microscopically image the local magnetic fields and magnetic susceptibility near the surface of UTe$_2$, observing a homogeneous superfluid density $n_s$ and homogeneous pinned vortices. The temperature dependence of $n_s$ is consistent with an anisotropic gap and shows no evidence for an additional kink that would be expected at any second phase transition. Our findings are consistent with a dominant $B_{3u}$ superconducting order parameter in the case of a quasi-2D Fermi surface and provide no evidence for multiple phase transitions in $n_s(T)$ in UTe$_2$.

cond-mat.supr-con↗

arXiv2022

Thermodynamic and electrical transport properties of UTe$_2$ under uniaxial stress

Despite intense experimental efforts, the nature of the unconventional superconducting order parameter of UTe$_2$ remains elusive. This puzzle stems from different reported numbers of superconducting transitions at ambient pressure, as well as a complex pressure-temperature phase diagram. To bring new insights into the superconducting properties of UTe$_2$, we measured the heat capacity and electrical resistivity of single crystals under compressive uniaxial stress $σ$ applied along different crystallographic directions. We find that the critical temperature $T_{\rm c}$ of the single observed bulk superconducting transition decreases with $σ$ along $[100]$ and $[110]$ but increases with $σ$ along $[001]$. Aside from its effect on $T_{\rm c}$, we notice that $c$-axis stress leads to a significant piezoresistivity, which we associate with the shift of the zero-pressure resistivity peak at $T^\star \approx 15\, \rm K$ to lower temperatures under stress. Finally, we show that an in-plane shear stress $σ_{xy}$ does not induce any observable splitting of the superconducting transition over a stress range of $σ_{xy}\approx 0.17 \, \rm GPa$. This result suggests that the superconducting order parameter of UTe$_2$ may be single-component at ambient pressure.

cond-mat.supr-con↗

arXiv2022

Surface and electronic structure at atomic length scales of the non-symmorphic antiferromagnet Eu$_5$In$_2$Sb$_6$

We performed Scanning Tunneling Microscopy and Spectroscopy (STM/STS) measurements to investigate the Zintl phase Eu$_5$In$_2$Sb$_6$, a non-symmorphic antiferromagnet. The theoretical prediction of a non-trivial Fermi surface topology stabilized by the non-symmorphic symmetry motivated our research. On the cleaved (010) plane, we obtained striped patterns that can be correlated to the stacking of the [In$_2$Sb$_6$]$^{10-}$ double chains along the crystallographic $c$ axis. The attempted cleavage along the $a$ axis revealed a more complex pattern. We combined the STS measurement on non-reconstructed (010) and (081) surfaces with DFT calculations to further elucidate the electronic structure of Eu$_5$In$_2$Sb$_6$. From our investigations so far, direct experimental evidence of the predicted topological surface states remains elusive.

cond-mat.str-el↗

arXiv2022

Probing FeSi, a d-electron topological Kondo insulator candidate, with magnetic field, pressure, and microwaves

Recently, evidence for a conducting surface state below 19 K was reported for the correlated d-electron small gap semiconductor FeSi. In the work reported herein, the conducting surface state and the bulk phase of FeSi were probed via electrical resistivity measurements as a function of temperature T, magnetic field B to 60 T and pressure P to 7.6 GPa, and by means of a magnetic field modulated microwave spectroscopy (MFMMS) technique. The properties of FeSi were also compared to those of the Kondo insulator SmB6 to address the question of whether FeSi is a d-electron analogue of an f-electron Kondo insulator and, in addition, a topological Kondo insulator. The overall behavior of the magnetoresistance MR of FeSi at temperatures above and below the onset temperature (T_S) 19 K of the conducting surface state is similar to that of SmB6. The two energy gaps, inferred from the resistivity data in the semiconducting regime, increase with pressure up to about 7 GPa, followed by a drop which coincides with a sharp suppression of T_S. This behavior is similar to that reported for SmB6, except that the two energy gaps in SmB6 decrease with pressure before dropping abruptly at T_S. The MFMMS measurements showed a sharp feature at T_S (19 K) for FeSi, but no such feature was observed at T_S 4.5 K for SmB6. The absence of a feature at T_S for SmB6 may be due to experimental issues and will be the subject of a future investigation.

cond-mat.str-el↗

arXiv2022

Anisotropy of Kondo-lattice coherence in momentum space for CeCoIn5

We study the electronic and phononic excitations of heavy-fermion metal CeCoIn$_5$ by polarization-resolved Raman spectroscopy to explore the Kondo-lattice coherence. Below the coherence temperature T*\,=\,45\,K, the continuum of electronic excitations in the XY scattering geometry is suppressed at frequencies below 50\,cm$^{-1}$, whereas the low-frequency continuum in the X'Y' geometry exhibits no change across T*. We relate the suppression to the reduced electron-electron scattering rate resulting from the coherence effect. The presence of suppression in the XY geometry and absence of it in the X'Y' geometry implies that the $α$ and $β$ bands become coherent below T*, whereas the $γ$ band remains largely incoherent down to 10\,K. Moreover, two optical phonon modes exhibit anomalies in their temperature dependence of the frequency and linewidth below T*, which results from developing coherent spectral weight near the Fermi level and reduced electron-phonon scattering rate. Our results further support the key role of anisotropic hybridization in CeCoIn$_5$.

cond-mat.str-el↗

arXiv2021

Robust narrow-gap semiconducting behavior in square-net La$_{3}$Cd$_{2}$As$_{6}$

ABSTRACT: Narrow-gap semiconductors are sought-after materials due to their potential for long-wavelength detectors, thermoelectrics, and more recently non-trivial topology. Here we report the synthesis and characterization of a new family of narrow-gap semiconductors, $R$$_{3}$Cd$_{2}$As$_{6}$ ($R=$ La, Ce). Single crystal x-ray diffraction at room temperature reveals that the As square nets distort and Cd vacancies order in a monoclinic superstructure. A putative charge-density ordered state sets in at 279~K in La$_{3}$Cd$_{2}$As$_{6}$ and at 136~K in Ce$_{3}$Cd$_{2}$As$_{6}$ and is accompanied by a substantial increase in the electrical resistivity in both compounds. The resistivity of the La member increases by thirteen orders of magnitude on cooling, which points to a remarkably clean semiconducting ground state. Our results suggest that light square net materials within a $I4/mmm$ parent structure are promising clean narrow-gap semiconductors.

cond-mat.mtrl-sci↗

arXiv2021

Phase stability in SmB$_6$

We investigate flux-grown Sm-deficient Sm$_x$B$_6$ ($x < 1$) by global and local tools, including X-ray diffraction (XRD), electronic transport, and scanning tunneling microscopy (STM) and spectroscopy (STS). All these tools indicate a remarkable persistence of the SmB$_6$ local structure in the flux-grown samples even for nominal Sm concentrations as low as $x=0.75$. As a consequence, the overall electronic properties of Sm$_x$B$_6$, and particularly the surface conductance at low temperature, is only affected locally by the Sm-deficiency.

cond-mat.mtrl-sci↗

arXiv2021

Systematic manipulation of the surface conductivity of SmB$_6$

We show that the resistivity plateau of SmB$_6$ at low temperature, typically taken as a hallmark of its conducting surface state, can systematically be influenced by different surface treatments. We investigate the effect of inflicting an increasing number of hand-made scratches and microscopically defined focused ion beam-cut trenches on the surfaces of flux-grown Sm$_{1-x}$Gd$_x$B$_6$ with $x =$ 0, 0.0002. Both treatments increase the resistance of the low-temperature plateau, whereas the bulk resistance at higher temperature largely remains unaffected. Notably, the temperature at which the resistance deviates from the thermally activated behavior decreases with cumulative surface damage. These features are more pronounced for the focused ion beam treated samples, with the difference likely being related to the absence of microscopic defects like subsurface cracks. Therefore, our method presents a systematic way of controlling the surface conductance.

cond-mat.mtrl-sci↗

arXiv2021

Observation of nearly identical superconducting transition temperatures in pressurized Weyl semimetal MIrTe4 (M=Nb and Ta)

Here we report the observation of pressure-induced superconductivity in type-II Weyl semimetal (WSM) candidate NbIrTe4 and the evolution of its Hall coefficient (RH), magnetoresistance (MR), and lattice with increasing pressure to ~57 GPa. These results provide a significant opportunity to investigate the universal high-pressure behavior of ternary WSMs, including the sister compound TaIrTe4 that has been known through our previous studies. We find that the pressure-tuned evolution from the WSM to the superconducting (SC) state in these two compounds exhibit the same trend, i.e., a pressure-induced SC state emerges from the matrix of the non-superconducting WSM state at ~ 27 GPa, and then the WSM state and the SC state coexist up to 40 GPa. Above this pressure, an identical high-pressure behavior, characterized by almost the same value of RH and MR in its normal state and the same value of Tc in its SC state, appears in both compounds. Our results not only reveal a universal connection between the WSM state and SC state, but also demonstrate that NbIrTe4 and TaIrTe4 can make the same contribution to the normal and SC states that inhabit in the high-pressure phase, although these two compounds have dramatically different topological band structure at ambient pressure.

cond-mat.supr-con↗

arXiv2021

Thermal and magnetoelastic properties of α-RuCl3 in the field-induced low temperature states

We discuss the implications that new magnetocaloric, thermal expansion and magnetostriction data in $α$-RuCl$_{3}$ single crystals have on its temperature-field phase diagram and uncover the magnetic-field dependence of an apparent energy gap structure $Δ(H)$ that evolves when the low temperature antiferromagnetic order is suppressed. We show that, depending on how the thermal expansion data is modeled, $Δ(H)$ can show a cubic field dependence and remain finite at zero field, consistent with the pure Kitaev model hosting itinerant Majorana fermions and localized $\mathbb{Z}_{2}$ fluxes. Our magnetocaloric effect data provides, below $1\,\mathrm{K}$, unambiguous evidence for dissipative phenomena at $H_{\mathrm{c}}$, smoking gun for a first order phase transition. Our results, on the other hand, show little support for a phase transition from a QSL to a polarized paramagnetic state above $H_{\mathrm{c}}$.

cond-mat.str-el↗

arXiv2020

Bulk transport paths through defects in floating zone and Al flux grown SmB$_6$

We investigate the roles of disorder on low-temperature transport in SmB$_6$ crystals grown by both the Al flux and floating zone methods. We used the inverted resistance method with Corbino geometry to investigate whether low-temperature variations in the standard resistance plateau arises from a surface or a bulk channel in floating zone samples. The results show significant sample-dependent residual bulk conduction, in contrast to smaller amounts of residual bulk conduction previously observed in Al flux grown samples with Sm vacancies. We consider hopping in an activated impurity band as a possible source for the observed bulk conduction, but it is unlikely that the large residual bulk conduction seen in floating zone samples is solely due to Sm vacancies. We therefore propose that one-dimensional defects, or dislocations, contribute as well. Using chemical etching, we find evidence for dislocations in both flux and floating zone samples, with higher dislocation density in floating zone samples than in Al flux grown samples. In addition to the possibility of transport through one-dimensional dislocations, we also discuss our results in the context of recent theoretical models of SmB$_6$.

cond-mat.str-el↗

arXiv2020

Bulk and surface properties of SmB6

Samarium hexaboride crystallizes in a simple cubic structure (space group #221, Pm-3m), but its properties are far from being straightforward. Initially classified as a Kondo insulator born out of its intriguing intermediate valence ground state, SmB6 has been recently predicted to be a strongly correlated topological insulator. The subsequent experimental discovery of surface states has revived the interest in SmB6, and our purpose here is to review the extensive and in many aspects perplexing experimental record of this material. We will discuss both surface and bulk properties of SmB6 with an emphasis on the role of crystal growth and sample preparation. We will also highlight the remaining mysteries and open questions in the field.

cond-mat.str-el↗

arXiv2020

Comparative Scanning Tunneling Microscopy Study on Hexaborides

We compare STM investigations on two hexaboride compounds, SmB$_6$ and EuB$_6$, in an effort to provide a comprehensive picture of their surface structural properties. The latter is of particular importance for studying the nature of the surface states in SmB$_6$ by surface-sensitive tools. Beyond the often encountered atomically rough surface topographies of {\it in situ}, low-temperature cleaved samples, differently reconstructed as well as B-terminated and, more rarely, rare-earth terminated areas could be found. With all the different surface topographies observed on both hexaborides, a reliable assignment of the surface terminations can be brought forward.

cond-mat.mtrl-sci↗