АМ

А. М. Никитин

Vifor Pharma (Switzerland)

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

A. de Visser

University of Amsterdam

Y. K. Huang

University of Amsterdam

H.‐H. Klauß

TU Dresden

V. Grinenko

Shanghai Jiao Tong University

Rajib Sarkar

TU Dresden

Takashi Naka

National Institute for Materials Science

Yu Pan

Max Planck Institute for Chemical Physics of Solids

Clifford W. Hicks

University of Birmingham

A. P. Mackenzie

Max Planck Institute for Chemical Physics of Solids

Shreenanda Ghosh

TU Dresden

Cooperative Institutions

University of Amsterdam

Max Planck Institute for Chemical Physics of Solids

Paul Scherrer Institute

National Institute for Materials Science

Leibniz Institute for Solid State and Materials Research

University of Birmingham

University of St Andrews

TU Dresden

Vifor Pharma (Switzerland)

University of Cambridge

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

On the phase diagram of the superconducting ferromagnet UCoGe and other unconventional superconductors

А. М. Никитин

Superconductivity has inspired many scientists all around the world in the past hundred years. The mechanism which causes superconductivity was investigated in detail. Nevertheless, up to now, there is no unifying theory which can describe all the different types of superconductors. Therefore, it is important to collect empirical knowledge of special cases of superconductivity that have emerged in exotic materials in recent years. This thesis is dedicated to an experimental investigation of two fascinating classes of superconductors. The member of the first class, UCoGe, belongs to the family of heavy-fermion system. In this compound, superconductivity forms unexpectedly within the ferromagnetic phase. This makes it a unique laboratory tool to study the experimental realization of equal-spin paring superconductivity. The second type of studied superconductors is topological superconductors: SrxBi2Se3 and HoPdBi. These compounds belong to the family of materials which exhibit a non-trivial band inversion. The combination of the topological band structure and superconductivity can potentially be applied in spintronics and quantum computation. The main experimental techniques used in the thesis are electron transport and thermal expansion. An important part of the thesis project was devoted to the design and construction of a dilatometer with very high sensitivity that could be rotated in the magnetic field.

Source

Cite

Citations (0)

Rotational symmetry breaking in the topological superconductor SrxBi2Se3 probed by upper-critical field experiments

Scientific Reports (2016)

Yiming Pan А. М. Никитин G. K. Araizi Yingyi Huang Yoshitaka Matsushita

Abstract Recently it was demonstrated that Sr intercalation provides a new route to induce superconductivity in the topological insulator Bi 2 Se 3 . Topological superconductors are predicted to be unconventional with an odd-parity pairing symmetry. An adequate probe to test for unconventional superconductivity is the upper critical field, B c 2 . For a standard BCS layered superconductor B c 2 shows an anisotropy when the magnetic field is applied parallel and perpendicular to the layers, but is isotropic when the field is rotated in the plane of the layers. Here we report measurements of the upper critical field of superconducting Sr x Bi 2 Se 3 crystals ( T c = 3.0 K). Surprisingly, field-angle dependent magnetotransport measurements reveal a large anisotropy of B c 2 when the magnet field is rotated in the basal plane. The large two-fold anisotropy, while six-fold is anticipated, cannot be explained with the Ginzburg-Landau anisotropic effective mass model or flux flow induced by the Lorentz force. The rotational symmetry breaking of B c 2 indicates unconventional superconductivity with odd-parity spin-triplet Cooper pairs (Δ 4 -pairing) recently proposed for rhombohedral topological superconductors, or might have a structural nature, such as self-organized stripe ordering of Sr atoms.

Critical field

Topological insulator

10.1038/srep28632

Cite

Citations (147)

An approach to the zeta function of a finite factorgraph via the Markov topological chains

Journal of Mathematical Sciences (1997)

А. М. Никитин

Finite graph

Topological graph theory

Bibliography

10.1007/bf02355331

Cite

Citations (0)

Macroscopic phase separation of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2−x Se x revealed by μSR

Scientific Reports (2017)

А. М. Никитин V. Grinenko Rajib Sarkar Jean‐Christophe Orain M. V. Salis

Abstract The compound Sr 0.5 Ce 0.5 FBiS 2 belongs to the intensively studied family of layered BiS 2 superconductors. It attracts special attention because superconductivity at T sc = 2.8 K was found to coexist with local-moment ferromagnetic order with a Curie temperature T C = 7.5 K. Recently it was reported that upon replacing S by Se T C drops and ferromagnetism becomes of an itinerant nature. At the same time T sc increases and it was argued superconductivity coexists with itinerant ferromagnetism. Here we report a muon spin rotation and relaxation study (μSR) conducted to investigate the coexistence of superconductivity and ferromagnetic order in Sr 0.5 Ce 0.5 FBiS 2− x Se x with x = 0.5 and 1.0. By inspecting the muon asymmetry function we find that both phases do not coexist on the microscopic scale, but occupy different sample volumes. For x = 0.5 and x = 1.0 we find a ferromagnetic volume fraction of ~8 % and ~30 % at T = 0.25 K, well below T C = 3.4 K and T C = 3.3 K, respectively. For x = 1.0 ( T sc = 2.9 K) the superconducting phase occupies most (~64 %) of the remaining sample volume, as shown by transverse field experiments that probe the Gaussian damping due to the vortex lattice. We conclude ferromagnetism and superconductivity are macroscopically phase separated.

Muon spin spectroscopy

10.1038/s41598-017-17637-y

Cite

Citations (2)

Superconducting and ferromagnetic phase diagram of UCoGe probed by thermal expansion

Physical review. B./Physical review. B (2017)

А. М. Никитин J. J. Geldhof Y. K. Huang Dai Aoki A. de Visser

The superconducting ferromagnet UCoGe is a versatile laboratory tool to investigate the interplay of ferromagnetism (${T}_{\text{c}}$ = 3.0 K) and superconductivity (${T}_{\text{sc}}$ = 0.6 K). Here, the authors report the superconducting and magnetic phase diagram in the field-temperature plane determined by thermal expansion measurements. The use of the thermal expansion technique has the advantage that it involves a thermodynamic bulk probe. The experiments were carried out on a single crystal in fixed magnetic fields applied along the principal axes of the orthorhombic crystal. Since the phase diagram depends sensitively on the orientation of the magnetic field with respect to the crystal axes, the thermal expansion cell was mounted on a piezoelectric rotator to enable $i\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ tuning of the magnetic field angle. The authors observe that the Curie point for $B$ || $b$ shifts gradually to lower temperatures and present bulk-sensitive evidence for the unusual S-shaped ${B}_{\text{c2}}$ curve for the same field orientation. The results lend further support to theoretical proposals of spin-fluctuation mediated enhancement of superconductivity in a magnetic field ($B$ || $b$).

Orthorhombic crystal system

10.1103/physrevb.95.115151

Cite

Citations (3)

Composition induced metal–insulator quantum phase transition in the Heusler type Fe₂VAl

Journal of Physics Condensed Matter (2016)

Takashi Naka А. М. Никитин Yu Pan A. de Visser T. Nakane

We report the magnetism and transport properties of the Heusler compound Fe2+x V1-x Al at -0.10 ⩽ x ⩽ 0.20 under pressure and a magnetic field. A metal-insulator quantum phase transition occurred at x ≈ -0.05. Application of pressure or a magnetic field facilitated the emergence of finite zero-temperature conductivity σ 0 around the critical point, which scaled approximately according to the power law (P - P c ) (γ) . At x ⩽ -0.05, a localized paramagnetic spin appeared, whereas above the ferromagnetic quantum critical point at x ≈ 0.05, itinerant ferromagnetism was established. At the quantum critical points at x = -0.05 and 0.05, the resistivity and specific heat exhibited singularities characteristic of a Griffiths phase appearing as an inhomogeneous electronic state.

Heusler compound

Magnetism

Critical point (mathematics)

10.1088/0953-8984/28/28/285601

Cite

Citations (8)

Interaction between counter-propagating quantum Hall edge channels in the 3D topological insulator BiSbTeSe2

Physical review. B./Physical review. B (2017)

Chuan Li Bob de Ronde А. М. Никитин Y. K. Huang M. S. Golden

The quantum Hall effect is studied in the topological insulator ${\mathrm{BiSbTeSe}}_{2}$. By employing top- and back-gate electric fields at high magnetic field, the Landau levels of the Dirac cones in the top and bottom topological surface states can be tuned independently. When one surface is tuned to the electron-doped side of the Dirac cone and the other surface to the hole-doped side, the quantum Hall edge channels are counter-propagating. The opposite edge mode direction, combined with the opposite helicities of top and bottom surfaces, allows for scattering between these counter-propagating edge modes. The total Hall conductance is expected to be integer valued only when the scattering is strong. For weaker interaction, a noninteger quantum Hall effect is expected and indications for this effect are measured.

Topological insulator

Landau quantization

10.1103/physrevb.96.195427

Cite

Citations (21)

Split superconducting and time-reversal symmetry-breaking transitions in Sr2RuO4 under stress

Nature Physics (2021)

V. Grinenko Shreenanda Ghosh Rajib Sarkar Jean‐Christophe Orain А. М. Никитин

Muon spin spectroscopy

Chirality

T-symmetry

10.1038/s41567-021-01182-7

Cite

Citations (143)

Quantum oscillations of the topological surface states in low carrier concentration crystals of Bi2−xSbxTe3

Solid State Communications (2015)

Yu Pan А. М. Никитин Deyan Wu Y. K. Huang Alessandro Puri

Topological insulator

Crystal (programming language)

Surface States

10.1016/j.ssc.2015.11.008

Cite

Citations (6)

Rotational symmetry breaking in the topological superconductor Sr$_x$Bi$_2$Se$_3$ probed by upper-critical field experiments

arXiv (Cornell University) (2016)

Yiming Pan А. М. Никитин G. K. Araizi Yingyi Huang Yoshitaka Matsushita

Recently it was demonstrated that Sr intercalation provides a new route to induce superconductivity in the topological insulator Bi$_2$Se$_3$. Topological superconductors are predicted to be unconventional, with mixed even and odd parity Cooper pairs states. An adequate probe to test for unconventional superconductivity is the upper critical field, $B_{c2}$. For a standard BCS layered superconductor $B_{c2}$ shows an anisotropy when the magnetic field is applied parallel and perpendicular to the layers, but is isotropic when the field is rotated in the plane of the layers. Here we report measurements of the upper critical field of superconducting Sr$_x$Bi$_2$Se$_3$ crystals ($T_c = 3.0$~K). Surprisingly, field-angle dependent magnetotransport measurements reveal a large anisotropy of $B_{c2}$ when the magnet field is rotated in the basal plane. The large two-fold anisotropy, while six-fold is anticipated, cannot be explained with the Ginzburg-Landau anisotropic effective mass model or flux flow induced by the Lorentz force. The rotational symmetry breaking of $B_{c2}$ indicates unconventional superconductivity with an odd-parity polarized triplet Cooper pair state ($\Delta_4$-pairing) recently proposed for rhombohedral topological superconductors, or might have a structural nature, such as self-organized stripe ordering of Sr atoms.

Critical field

Topological insulator

Cooper pair

10.48550/arxiv.1603.04197

Cite

Citations (0)