Studies of electronic structure across a quantum phase transition in CeRhSb_{1-x}Sn_{x}

We study an electronic structure of CeRhSb1xSnx system, which displays quantum critical transition from a Kondo insulator to a non-Fermi liquid at x = 0:13. We provide ultraviolet photoelectron spectra of valence band obtained at 12.5 K. A coherent peak at the Fermi level is not present in the data, but a signal related to 4f1 7=2 nal state is detected. Spectral intensity at the Fermi edge has a general tendency to grow with Sn content. Theoretical calculations of band structure are realized with full-potential local-orbital minimum-basis code using scalar relativistic and full relativistic approach. The calculations reveal a depletion of density of states at the Fermi level for CeRhSb. This gap is shifted above the Fermi energy with increasing Sn content and thus a rise of density of states at the Fermi level is re ected in the calculations. It agrees with metallic properties of compounds with larger x. The calculations also yield another important e ect of Sn substitution. Band structure is displaced in a direction corresponding to hole doping, although with deviations from a rigid band shift scenario. Lifshitz transitions modify a topology of the Fermi surface a few times and a number of bands crossing the Fermi level increases

Dirac Dispersions and Fermi Surface Nesting in LaCuSb2_{2}

LaCuSb$_{2}$ is a superconductor with a transition temperature of about $T_\text{c} = 0.9$K and is a potential platform where Dirac fermions can be experimentally observed. In this paper, we report systematic high-resolution studies of its electronic structure using the angle-resolved photoemission spectroscopy (ARPES) technique supported by the DFT calculation. The Fermi surface consists of four branches, of which the two inner ones are more 3-dimensional and the theoretical calculations reproduce well the experiment. We observe several linear dispersions forming Dirac-like structures. The nodal lines are present in the system along ${\text{M}}$-${\text{A}}$ and ${\text{X}}$-${\text{R}}$ and Dirac crossings along ${\text{X}}$-${\text{R}}$ are observed by ARPES. Finally, the nesting between external Fermi surface pockets, which corresponds to charge density wave (CDW) modulation vector is enhanced in LaCuSb$_{2}$ as compared to LaAgSb$_{2}$, while CDW appears in the latter system

Electronic band structure and surface states in Dirac semimetal LaAgSb2LaAgSb_{2}

LaAgSb$_{2}$ is a Dirac semimetal showing charge density wave (CDW) order. Previous angle-resolved photoemission spectroscopy (ARPES) results suggest the existence of the Dirac-cone-like structure in the vicinity of the Fermi level along the $\Gamma$–M direction. This paper is devoted to a complex analysis of the electronic band structure of LaAgSb$_{2}$ by means of ARPES and theoretical studies within the ab initio method as well as tight binding model formulation. To investigate the possible surface states, we performed the direct DFT slab calculation and the surface Green function calculation for the (001) surface. The appearance of the surface states, which depends strongly on the surface, points to the conclusion that LaSb termination is realized in the cleaved crystals. Moreover, the surface states predicted by our calculations at the $\Gamma$ and X points are found by ARPES. Nodal lines, which exist along the X–R and M–A paths due to crystal symmetry, are also observed experimentally. The calculations reveal other nodal lines, which originate from the vanishing of spin–orbit splitting and are located at the X–M–A–R plane at the Brillouin zone boundary. In addition, we analyze the band structure along the $\Gamma$–M path to verify whether Dirac surface states can be expected. Their appearance in this region is not confirmed

A novel ferroelectric Rashba semiconductor

Fast, reversible, and low-power manipulation of the spin texture is crucial for next generation spintronic devices like non-volatile bipolar memories, switchable spin current injectors or spin field effect transistors. Ferroelectric Rashba semiconductors (FERSC) are the ideal class of materials for the realization of such devices. Their ferroelectric character enables an electronic control of the Rashba-type spin texture by means of the reversible and switchable polarization. Yet, only very few materials are established to belong to this class of multifunctional materials. Here, Pb$_{1−x}$Ge$_{x}$Te is unraveled as a novel FERSC system down to nanoscale. The ferroelectric phase transition and concomitant lattice distortion are demonstrated by temperature dependent X-ray diffraction, and their effect on electronic properties are measured by angle-resolved photoemission spectroscopy. In few nanometer-thick epitaxial heterostructures, a large Rashba spin-splitting is exhibiting a wide tuning range as a function of temperature and Ge content. This work defines Pb$_{1−x}$Ge$_{x}$Te as a high-potential FERSC system for spintronic applications

Intercalation-induced states at the Fermi level and the coupling of intercalated magnetic ions to conducting layers in Ni1/3_{1/3}NbS2_2

The magnetic sublayers introduced by intercalation into the host transition-metal dichalcogenide (TMD) are known to produce various magnetic states. The magnetic sublayers and their magnetic ordering strongly modify the electronic coupling between layers of the host compound. Understanding the roots of this variability is a significant challenge. Here we employ the angle-resolved photoelectron spectroscopy at various photon energies, the {\it ab initio} electronic structure calculations, and modeling to address the particular case of Ni-intercalate, Ni$_{1/3}$NbS$_2$. We find that the bands around the Fermi level bear the signature of a strong yet unusual hybridization between NbS$_2$ conduction band states and the Ni 3$d$ orbitals. The hybridization between metallic NbS$_2$ layers is almost entirely suppressed in the central part of the Brillouin zone, including the part of the Fermi surface around the $\mathrm{\Gamma}$ point. Simultaneously, it gets very pronounced towards the zone edges. It is shown that this behavior is the consequence of the rather exceptional, {\it symmetry imposed}, spatially strongly varying, {\it zero total} hybridization between relevant Ni magnetic orbitals and the neighboring Nb orbitals that constitute the metallic bands. We also report the presence of the so-called $\beta$-feature, discovered only recently in two other magnetic intercalates with very different magnetic orderings. In Ni$_{1/3}$NbS$_2$, the feature shows only at particular photon energies, indicating its bulk origin. Common to prior observations, it appears as a series of very shallow electron pockets at the Fermi level, positioned along the edge of the Brillouin zone. Unforeseen by {\it ab initio} electronic calculations, and its origin still unresolved, the feature appears to be a robust consequence of the intercalation of 2H-NbS$_2$ with magnetic ions.Comment: 14 pages, 7 figures with subfigures, 53 references, supplemental material uploaded as the separate pdf fil

3D Topological Semimetal Phases of Strained α\alpha-Sn on Insulating Substrate

$\alpha$-Sn is an elemental topological material, whose topological phases can be tuned by strain and magnetic field. Such tunability offers a substantial potential for topological electronics. However, InSb substrates, commonly used to stabilize $\alpha$-Sn allotrope, suffer from parallel conduction, restricting transport investigations and potential applications. Here, the successful MBE growth of high-quality $\alpha$-Sn layers on insulating, hybrid CdTe/GaAs(001) substrates, with bulk electron mobility approaching 20000 cm$^2$V$^{-1}$s$^{-1}$ is reported. The electronic properties of the samples are systematically investigated by independent complementary techniques, enabling thorough characterization of the 3D Dirac (DSM) and Weyl (WSM) semimetal phases induced by the strains and magnetic field, respectively. Magneto-optical experiments, corroborated with band structure modeling, provide an exhaustive description of the bulk states in the DSM phase. The modeled electronic structure is directly observed in angle-resolved photoemission spectroscopy, which reveals linearly dispersing bands near the Fermi level. The first detailed study of negative longitudinal magnetoresistance relates this effect to the chiral anomaly and, consequently, to the presence of WSM. Observation of the $\pi$ Berry phase in Shubnikov-de Haas oscillations agrees with the topologically non-trivial nature of the investigated samples. Our findings establish $\alpha$-Sn as an attractive topological material for exploring relativistic physics and future applications.Comment: Main text: 35 pages, 7 figures; Supplementary Materials: 22 pages, 12 figure

SOLARIS National Synchrotron Radiation Centre in Krakow, Poland

The SOLARIS synchrotron located in Krakow, Poland, is a third-generation light source operating at medium electron energy. The first synchrotron light was observed in 2015, and the consequent development of infrastructure lead to the first users’ experiments at soft X-ray energies in 2018. Presently, SOLARIS expands its operation towards hard X-rays with continuous developments of the beamlines and concurrent infrastructure. In the following, we will summarize the SOLARIS synchrotron design, and describe the beamlines and research infrastructure together with the main performance parameters, upgrade, and development plans

Studies of the electronic structure of superconducting FeTe0.65Se0.35 by means of photoemission spectroscopy

W niniejszej pracy wyznaczono strukturę pasmową nadprzewodnika o składzie FeTe0.65Se0.35 wzdłuż kierunku "Γ-M" przy użyciu metody kątoworozdzielczej spektroskopii fotoemisyjnej (ARPES). W rejonie punktu Γ zaobserwowano trzy kieszenie dziurowe. Nie udało się zaobserwować kieszeni elektronowych w rejonie punktu M. Wykonano pomiar rentgenowskiej spektroskopii fotoemisyjnej (XPS), który pokazał skład pierwiastkowy badanej próbki. Widoczne są linie spektralne pochodzące od żelaza, telluru, selenu oraz pierwiastków znajdujących się w otoczeniu badanego monokryształu.In this work the band structure of superconducting FeTe0.65Se0.35 has been determined along the direction of "Γ-M" by means of angle-resolved photoemission spectroscopy (ARPES). In the region of the Γ point three hole pockets have been observed. Electron pockets in the region of the M point could not be resolved. An elemental composition of the sample has been determined by X-ray photoemission spectroscopy (XPS) measurement. It was possible to observe spectral lines of Fe, Te, Se and elements located in the vicinity of the investigated crystal

Influence of nickel and cobalt doping on electronic structure of a FeTe0.65Se0.35 superconductor

W niniejszej pracy zbadano strukturę elektronową nadprzewodnika FeTe0.65Se0.35 o temperaturze krytycznej równej ok. 14K, oraz dwóch związków o składzie FeNi0.055Te0.65Se0.35 i FeCo0.1Te0.65Se0.35, w których nie obserwuje się nadprzewodnictwa. Za pomocą kątowo rozdzielczej spektroskopii fotoemisyjnej (ARPES) wykonano mapy powierzchni Fermiego, mapy powierzchni izoenergetycznych w zakresie energii od 10 meV powyżej energii Fermiego do 75 meV poniżej energii Fermiego oraz wyznaczono relacje dyspersji wzdłuż kierunku Γ-M. Zaobserwowano zwiększanie się części powierzchni Fermiego o charakterze elektronowym, zmniejszanie się dziurowej powierzchni Fermiego oraz przesuwanie się pasm na skutek domieszkowania układu. Wykonano pomiar rentgenowskiej spektroskopii fotoemisyjnej (XPS), który pokazał skład pierwiastkowy badanych związków oraz wyznaczono przesuniecie linii Fe 2p na skutek domieszkowania niklem.In this work we have investigated the electronic structure of a FeTe0.65Se0.35 superconductor, with a critical temperature of 14 K, and Ni and Co doped system (FeNi0.055Te0.65Se0.35, FeCo0.1Te0.65Se0.35) with suppressed superconductivity. Studies performed by means of the angle resolved photoemission spectroscopy (ARPES) have revealed the band structure along Γ-M direction, the Fermi surface and isoenergetic surfaces. Data from the experiment have shown that Ni and Co doping shifts the Fermi level upwards, decreases the hole like Fermi surface and increases the electron like Fermi surface.An elemental composition of the samples has been determined by X-ray photoemission spectroscopy (XPS) measurement. We have found out that Ni doping shifts Fe 2p spectral lines