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Zhou L, He Q, Que X, Rost AW, Takagi H. A spectroscopic-imaging scanning tunneling microscope in vector magnetic field. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2023; 94:033704. [PMID: 37012779 DOI: 10.1063/5.0131532] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Accepted: 02/15/2023] [Indexed: 06/19/2023]
Abstract
Cryogenic scanning tunneling microscopy and spectroscopy (STM/STS) performed in a high vector magnetic field provide unique possibilities for imaging surface magnetic structures and anisotropic superconductivity and exploring spin physics in quantum materials with atomic precision. Here, we describe the design, construction, and performance of a low-temperature, ultra-high-vacuum (UHV) spectroscopic-imaging STM equipped with a vector magnet capable of applying a field of up to 3 T in any direction with respect to the sample surface. The STM head is housed in a fully bakeable UHV compatible cryogenic insert and is operational over variable temperatures ranging from ∼300 down to 1.5 K. The insert can be easily upgraded using our home-designed 3He refrigerator. In addition to layered compounds, which can be cleaved at a temperature of either ∼300, ∼77, or ∼4.2 K to expose an atomically flat surface, thin films can also be studied by directly transferring using a UHV suitcase from our oxide thin-film laboratory. Samples can be treated further with a heater and a liquid helium/nitrogen cooling stage on a three-axis manipulator. The STM tips can be treated in vacuo by e-beam bombardment and ion sputtering. We demonstrate the successful operation of the STM with varying the magnetic field direction. Our facility provides a way to study materials in which magnetic anisotropy is a key factor in determining the electronic properties such as in topological semimetals and superconductors.
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Affiliation(s)
- Lihui Zhou
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, Stuttgart 70569, Germany
| | - Qingyu He
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, Stuttgart 70569, Germany
| | - Xinglu Que
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, Stuttgart 70569, Germany
| | - Andreas W Rost
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, Stuttgart 70569, Germany
| | - Hide Takagi
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, Stuttgart 70569, Germany
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Signatures of bosonic Landau levels in a finite-momentum superconductor. Nature 2021; 599:51-56. [PMID: 34732867 DOI: 10.1038/s41586-021-03915-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Accepted: 08/16/2021] [Indexed: 11/08/2022]
Abstract
Charged particles subjected to magnetic fields form Landau levels (LLs). Originally studied in the context of electrons in metals1, fermionic LLs continue to attract interest as hosts of exotic electronic phenomena2,3. Bosonic LLs are also expected to realize novel quantum phenomena4,5, but, apart from recent advances in synthetic systems6,7, they remain relatively unexplored. Cooper pairs in superconductors-composite bosons formed by electrons-represent a potential condensed-matter platform for bosonic LLs. Under certain conditions, an applied magnetic field is expected to stabilize an unusual superconductor with finite-momentum Cooper pairs8,9 and exert control over bosonic LLs10-13. Here we report thermodynamic signatures, observed by torque magnetometry, of bosonic LL transitions in the layered superconductor Ba6Nb11S28. By applying an in-plane magnetic field, we observe an abrupt, partial suppression of diamagnetism below the upper critical magnetic field, which is suggestive of an emergent phase within the superconducting state. With increasing out-of-plane magnetic field, we observe a series of sharp modulations in the upper critical magnetic field that are indicative of distinct vortex states and with a structure that agrees with predictions for Cooper pair LL transitions in a finite-momentum superconductor10-14. By applying Onsager's quantization rule15, we extract the momentum. Furthermore, study of the fermionic LLs shows evidence for a non-zero Berry phase. This suggests opportunities to study bosonic LLs, topological superconductivity, and their interplay via transport16, scattering17, scanning probe18 and exfoliation techniques19.
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Devarakonda A, Inoue H, Fang S, Ozsoy-Keskinbora C, Suzuki T, Kriener M, Fu L, Kaxiras E, Bell DC, Checkelsky JG. Clean 2D superconductivity in a bulk van der Waals superlattice. Science 2020; 370:231-236. [DOI: 10.1126/science.aaz6643] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2019] [Accepted: 08/21/2020] [Indexed: 11/02/2022]
Abstract
Advances in low-dimensional superconductivity are often realized through improvements in material quality. Apart from a small group of organic materials, there is a near absence of clean-limit two-dimensional (2D) superconductors, which presents an impediment to the pursuit of numerous long-standing predictions for exotic superconductivity with fragile pairing symmetries. We developed a bulk superlattice consisting of the transition metal dichalcogenide (TMD) superconductor 2H-niobium disulfide (2H-NbS2) and a commensurate block layer that yields enhanced two-dimensionality, high electronic quality, and clean-limit inorganic 2D superconductivity. The structure of this material may naturally be extended to generate a distinct family of 2D superconductors, topological insulators, and excitonic systems based on TMDs with improved material properties.
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Affiliation(s)
- A. Devarakonda
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - H. Inoue
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - S. Fang
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
| | - C. Ozsoy-Keskinbora
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
| | - T. Suzuki
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - M. Kriener
- RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan
| | - L. Fu
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - E. Kaxiras
- Department of Physics, Harvard University, Cambridge, MA 02138, USA
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
| | - D. C. Bell
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
- Center for Nanoscale Systems, Harvard University, Cambridge, MA 02138, USA
| | - J. G. Checkelsky
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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4
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Barkman M, Samoilenka A, Babaev E. Surface Pair-Density-Wave Superconducting and Superfluid States. PHYSICAL REVIEW LETTERS 2019; 122:165302. [PMID: 31075028 DOI: 10.1103/physrevlett.122.165302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Revised: 02/03/2019] [Indexed: 06/09/2023]
Abstract
Fulde, Ferrell, Larkin, and Ovchinnikov (FFLO) predicted inhomogeneous superconducting and superfluid ground states, spontaneously breaking translation symmetries. In this Letter, we demonstrate that the transition from the FFLO to the normal state as a function of temperature or increased Fermi surface splitting is not a direct one. Instead, the system has an additional phase transition to a different state where pair-density-wave superconductivity (or superfluidity) exists only on the boundaries of the system, while the bulk of the system is normal. The surface pair-density-wave state is very robust and exists for much larger fields and temperatures than the FFLO state.
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Affiliation(s)
- Mats Barkman
- Department of Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - Albert Samoilenka
- Department of Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
| | - Egor Babaev
- Department of Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden
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Chen AQ, Park MJ, Gill ST, Xiao Y, Reig-I-Plessis D, MacDougall GJ, Gilbert MJ, Mason N. Finite momentum Cooper pairing in three-dimensional topological insulator Josephson junctions. Nat Commun 2018; 9:3478. [PMID: 30154472 PMCID: PMC6113236 DOI: 10.1038/s41467-018-05993-w] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 08/06/2018] [Indexed: 11/09/2022] Open
Abstract
Unconventional superconductivity arising from the interplay between strong spin–orbit coupling and magnetism is an intensive area of research. One form of unconventional superconductivity arises when Cooper pairs subjected to a magnetic exchange coupling acquire a finite momentum. Here, we report on a signature of finite momentum Cooper pairing in the three-dimensional topological insulator Bi2Se3. We apply in-plane and out-of-plane magnetic fields to proximity-coupled Bi2Se3 and find that the in-plane field creates a spatially oscillating superconducting order parameter in the junction as evidenced by the emergence of an anomalous Fraunhofer pattern. We describe how the anomalous Fraunhofer patterns evolve for different device parameters, and we use this to understand the microscopic origin of the oscillating order parameter. The agreement between the experimental data and simulations shows that the finite momentum pairing originates from the coexistence of the Zeeman effect and Aharonov–Bohm flux. Unconventional superconductivity may emerge from the interplay between strong spin–orbit coupling and magnetism. Here, Chen et al. report an anomalous Fraunhofer pattern in three-dimensional topological insulator Bi2Se3 and attribute it as a signature of finite momentum Cooper pairing.
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Affiliation(s)
- Angela Q Chen
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, 61801, IL, United States
| | - Moon Jip Park
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, 61801, IL, United States
| | - Stephen T Gill
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, 61801, IL, United States
| | - Yiran Xiao
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, 61801, IL, United States
| | - Dalmau Reig-I-Plessis
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, 61801, IL, United States
| | - Gregory J MacDougall
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, 61801, IL, United States
| | - Matthew J Gilbert
- Department of Electrical and Computer Engineering, University of Illinois, Urbana, 61801, IL, USA
| | - Nadya Mason
- Department of Physics and Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, 61801, IL, United States.
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In Search of Unambiguous Evidence of the Fulde–Ferrell–Larkin–Ovchinnikov State in Quasi-Low Dimensional Superconductors. CONDENSED MATTER 2017. [DOI: 10.3390/condmat2030030] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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7
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Liu CX. Unconventional Superconductivity in Bilayer Transition Metal Dichalcogenides. PHYSICAL REVIEW LETTERS 2017; 118:087001. [PMID: 28282184 DOI: 10.1103/physrevlett.118.087001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Indexed: 06/06/2023]
Abstract
Bilayer transition metal dichalcogenides (TMDs) belong to a class of materials with two unique features, the coupled spin-valley-layer degrees of freedom and the crystal structure that is globally centrosymmetric but locally noncentrosymmetric. In this Letter, we will show that the combination of these two features can lead to a rich phase diagram for unconventional superconductivity, including intralayer and interlayer singlet pairings and interlayer triplet pairings, in bilayer superconducting TMDs. In particular, we predict that the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov state can exist in bilayer TMDs under an in-plane magnetic field. We also discuss the experimental relevance of our results and possible experimental signatures.
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Affiliation(s)
- Chao-Xing Liu
- Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802-6300, USA
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Kargarian M, Efimkin DK, Galitski V. Amperean Pairing at the Surface of Topological Insulators. PHYSICAL REVIEW LETTERS 2016; 117:076806. [PMID: 27563988 DOI: 10.1103/physrevlett.117.076806] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2016] [Indexed: 06/06/2023]
Abstract
The surface of a 3D topological insulator is described by a helical electron state with the electron's spin and momentum locked together. We show that in the presence of ferromagnetic fluctuations the surface of a topological insulator is unstable towards a superconducting state with unusual pairing, dubbed Amperean pairing. The key idea is that the dynamical fluctuations of a ferromagnetic layer deposited on the surface of a topological insulator couple to the electrons as gauge fields. The transverse components of the magnetic gauge fields are unscreened and can mediate an effective interaction between electrons. There is an attractive interaction between electrons with momenta in the same direction which makes the pairing to be of Amperean type. We show that this attractive interaction leads to a p-wave pairing instability of the Fermi surface in the Cooper channel.
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Affiliation(s)
- Mehdi Kargarian
- Joint Quantum Institute and Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA
| | - Dmitry K Efimkin
- Joint Quantum Institute and Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA
| | - Victor Galitski
- Joint Quantum Institute and Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA
- School of Physics, Monash University, Melbourne, Victoria 3800, Australia
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Yang K. Realization and detection of Fulde-Ferrell-Larkin-Ovchinnikov superfluid phases in trapped atomic fermion systems. PHYSICAL REVIEW LETTERS 2005; 95:218903. [PMID: 16384194 DOI: 10.1103/physrevlett.95.218903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2005] [Indexed: 05/05/2023]
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Kaur RP, Agterberg DF, Sigrist M. Helical vortex phase in the noncentrosymmetric CePt3Si. PHYSICAL REVIEW LETTERS 2005; 94:137002. [PMID: 15904019 DOI: 10.1103/physrevlett.94.137002] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2004] [Indexed: 05/02/2023]
Abstract
We consider the role of magnetic fields on the broken inversion superconductor CePt3Si. We show that the upper critical field for a field along the c axis exhibits a much weaker paramagnetic effect than for a field applied perpendicular to the c axis. The in-plane paramagnetic effect is strongly reduced by the appearance of helical structure in the order parameter. We find that, to get good agreement between theory and recent experimental measurements of H(c2), this helical structure is required. We propose a Josephson junction experiment that can be used to detect this helical order. In particular, we predict that the Josephson current will exhibit a magnetic interference pattern for a magnetic field applied perpendicular to the junction normal. We also discuss unusual magnetic effects associated with the helical order.
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Affiliation(s)
- R P Kaur
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211, USA
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