Quantum oscillations in topological insulator microwires contacted with superconducting In2Bi leads

Here we studied the magnetoresistance (MR) of polycrystal Bi2Te2Se topological insulator (TI) microwires contacted with superconducting In2Bi leads. Bi2Te2Se has a simple band structure with a single Dirac cone on the surface and a large non-trivial bulk gap of 300 meV. To study the TI/SC interface, the Bi2Te2Se glass-coated microwire with a diameter of d = 17 µm was connected to copper leads on one side using superconducting alloy In2Bi (Tc=5.6 K), and on the other side using gallium. The topologically nontrivial 3D superconductor (SC) In2Bi has proximity-induced superconductivity of topological surface states. To eliminate conventional contribution to superconductivity from the bulk, the resulting edge states of the TI/SC contact area were studied in magnetic fields above Hc2 in In2Bi. The h/2e oscillations of magnetoresistance (MR) in longitudinal and transverse magnetic fields (up to 1 T) at the TI/SC interface were observed at various temperatures (4.2 K–1.5 K) [1,2]. To explain the observed oscillations, we used magnetic flux quantization, which requires a multiply connected geometry where flux can penetrate into normal regions surrounded by a superconductor. The effective width of the closed superconducting area of the TI/SC interface is determined to be 15 nm from an analysis of FFT spectra and the beats of the MR oscillations for two different directions (longitudinal and transverse) of magnetic field

Quantum Oscillations in Topological Insulator Bi2Te2Se Microwires Contacted with Superconducting In2Bi Leads

Acces full text - https://doi.org/10.1007/978-3-031-42775-6_33We studied the magnetoresistance (MR) of polycrystal Bi2Te2Se topological insulator (TI) microwires contacted with superconducting In2Bi leads. Bi2Te2Se has a simple band structure with a single Dirac cone on the surface and a large non-trivial bulk gap of 300 meV. To study the TI/SC interface, the Bi2Te2Se glass-coated microwire with a diameter of d = 17 µm was connected to copper leads on one side using superconducting alloy In2Bi (Tc = 5.6 K), and on the other side using gallium. The topologically nontrivial 3D superconductor (SC) In2Bi has proximity-induced superconductivity of topological surface states. To eliminate conventional contribution to superconductivity from the bulk, the resulting edge states of the TI/SC contact area were studied in magnetic fields above Hc2 in In2Bi. The h/2e oscillations of magnetoresistance (MR) in longitudinal and transverse magnetic fields (up to 1 T) at the TI/SC interface were observed at various temperatures (4.2 k–1.5 K). To explain the observed oscillations, we used magnetic flux quantization, which requires a multiply connected geometry where flux can penetrate into normal regions surrounded by a superconductor. The effective width of the closed superconducting area of the TI/SC interface is determined to be 15 nm from an analysis of FFT spectra and the beats of the MR oscillations for two different directions of magnetic field

Angle dependence of the magnetoresistance in bi nanowires

AbstractBulk bismuth has been classified as a trivial topological insulator (TI) where the surface states do not have topological protection. Still, the electronic mobility of surface states is exceptionally large. This is not surprising if we consider that bulk Bi can be assembled by stacking bilayers, and that the bilayer of Bi is thought to represent a two dimensional TI that supports edge modes propagating along the perimeter of the sample, modes that exhibit coherent propagation and suppression of backscattering

Transport properties of a topological Insulator based on Bi0.83Sb0.17 nanowires

We have investigated the transport properties of topological insulator based on single-crystal Bi0.83Sb0.17 nanowires. The single-crystal nanowire samples in the diameter range 200 nm – 1.1 μm were prepared by the high frequency liquid phase casting in a glass capillary using an improved Ulitovsky technique; they were cylindrical single-crystals with (1011) orientation along the wire axis. In this orientation, the wire axis makes an angle of 19.5o with the bisector axis C1 in the bisector-trigonal plane. Bi0.83Sb0.17 is a narrow gap semiconductor with energy gap at L point of Brillouin zone ΔE= 21 meV. In accordance with the measurements of the temperature dependence of the resistivity of the samples resistance increases with decreasing temperature, but at low temperatures decrease in the resistance is observed. This effect, decrease in the resistance, is a clear manifestation of the interesting properties of topological insulators - the presence on its surface of a highly conducting zone. The Arrhenius plot of R in samples d=1.1 μm and d=200 nm indicates a thermal activation behavior with an activation gap ΔE= 21 and 40 meV, respectively, which proves the presence of the quantum size effect in these samples. We found that in the range of diameter 1100 nm - 200 nm when the diameter decreases the energy gap is growing exponentially. We have investigated magnetoresistance of Bi0.83Sb0.17 nanowires at various magnetic field orientations. From the temperature dependences of Shubnikov de Haas oscillation amplitude for different orientation of magnetic field we have calculated the cyclotron mass mc and Dingle temperature TD for longitudinal and transverse (B||C3 and B||C2) directions of magnetic fields, which equal 1.96*10-2 m0, 9.8 K, 8.5*10-3 m0 , 9.4 K and 1.5*10-1 m0 , 2.8 K respectively. The observed effect are discussed

Magneto- seebeck coefficient Bi1-XSbX microwires for thermoelectric applications

AbstractDue to development of new concepts such as the low- dimensional structures [1] and influence the quantum confinement of change carrier acoustic phonon –boundary scattering for increase figure of merit ZT=2/(T) opened up a completely different strategy for ZT enhancement in one- dimensional structures [1]. We study the thermoelectric properties of Bi1-xSbx in semimetal and semiconductor wires with different diameter in the presence of magnetic field in the temperature range 4.2- 300 K

Some urgent problems of electrophysical properties of bismuth and its alloys

Last years bismuth and its alloys attract great attention of a wide circle of researchers. This is determined first of all by the fact that in low dimensional structures based on bismuth one can expect significant increasing of thermoelectric efficiency Z in the low temperature region. Construction of these systems, if it is realizable, would considerably increase possibilities of cryogenic electronics, especially the one based on high temperature superconductors. For this purpose it is necessary to solve a number of complicated technological, applied and fundamental scientific problems, this implying significant extension of spectrum of scientific researches. The main aim of the present report is to draw attention to a number of the most important problems standing in the way of increasing of applied parameters of bismuth based structures

Electrical and thermoelectric properties of semiconducting Bi1-xSbx nanowires

In this paper we shall present the results obtained with measurements of transport effects in semiconducting Bi1-xSbx single crystal wires in glass cover, prepared by liquid phase casting, using the improved Ulitovsky method. The measurement included the electrical resistivity, Seebeck coefficient as functions of temperature, magnetic field and diameter wires. The wires diameters ranging from 100 nm to 1000 nm. The data were taken between 1.5- 300 K in magnetic field up to 15 T. The temperature dependences resistance R(T) and thermopower show the significant dependences on the wire diameters in low temperature region. We observed the quantum oscillations only in thin Bi-17at%Sb wires in longitudinal and transverse directions. In the thin (200 nm) Bi-17%Sb wires a sharp deviation from exponential temperature behavior resistance R(T) characteristic of bulk semiconductor is observed. The results are discussed in the context of the state the topological insulator and the influence of the surface state on the electronic properties of semiconducting Bi1-xSbx nanowires

Anisotropy and size effects in Bi1-xSbx semiconductor wires in a magnetic field

The electron transport and longitudinal and transverse magnetoresistance (MR) of glass-insulated Bi0.92Sb0.08 single-crystal wires with diameters of 180 nm to 2.2 μm and the (1011) orientation along the wire axis have been studied. The wires have been prepared by liquid-phase casting. It has been first found that the energy gap ΔE increases by a factor of 4 with a decrease in wire diameter d due to the manifestation of the quantum size effect, which can occur under conditions of a linear energy–momentum dispersion law characteristic of both the gapless state and the surface states in topological insulators (TIs). It has been revealed that, in strong magnetic fields at low temperatures, a semiconductor–semimetal transition occurs, which is evident as an anomalous decrease in the transverse MR anisotropy and the appearance of a metallic temperature dependence of resistance at T < 100 K. It has been found that the effect of negative MR, the appearance of an anomalous maximum in the longitudinal MR, and the dependence of Hmax ~ d-1 at 4.2 K is a manifestation of the classical MacDonald–Chambers size effect. The calculated value of the component of the Fermi momentum perpendicular to the magnetic induction vector H is 2 times higher than the value for pure bismuth wires. The features of the manifestation of the quantum size effect in Bi0.92Sb0.08 wires, semiconductor–semimetal electronic transitions induced by a magnetic field, and a decrease in the transverse MR anisotropy indicate the occurrence of new effects in low-dimensional structures based on semiconductor wire TIs, which require new scientific approaches and applications.A fost studiat transportul de electroni și magnetoresistența longitudinală și transversală (MR) a firelor monocristaline de Bi0.9Sb0.08 în înveliș de sticlă cu diametre de la 180 nm până la 2,2 μm și orientarea (1011) de-a lungul axei firului. Firele au fost obtinute prin turnarea din faza lichidă. Pentru prima dată s-a constatat că gap-ul energetic E crește de 4 ori cu micșorarea diametrului firului d, datorită manifestării efectelor cuantice dimensionale, care pot apărea în condițiile unei legi de dispersie energie-impuls liniare, care este caracteristică atât pentru o stare fără gap, cât și pentru stările de suprafață în izolatorii topologici (TIs). S-a observat că, în câmpurile magnetice puternice la temperaturi scăzute, se produce o tranziție semiconductor-semimetal, care se manifestă printr-o scădere anormală a anizotropiei magnetoresistenței transversale și apariția unei dependențe metalice de temperatură a rezistenței la T<100K. S-a constatat că efectul magnetoresistenței negative, apariția unui maxim anormal în magnetoresistența longitudinală și dependența Hmax ~ d～1 la 4,2 K sunt o manifestare a efectului dimensional clasic MacDonald-Chambers. Valoarea calculată a componentei - a impulsului Fermi, perpendicular pe vectorul de inducție magnetică H, este de 2 ori mai mare decât valoarea pentru firele de bismut pur. Particularitățile manifestării efectului cuantic dimensional în firele Bi0,92Sb0,08, tranzițiile electronice semiconductor-semimetal induse de un câmp magnetic și scăderea anizotropiei magnetoresistenței transversale indică la manifestarea de noi efecte în structurile de dimensiuni reduse ale izolatorilor topologici pe fire semiconductoare, care necesită noi abordări științifice și aplicații