Giant magnetochiral anisotropy from quantum confined surface states of topological insulator nanowires

Legg, Henry F.; Rößler, Matthias; Münning, Felix; Fan, Dingxun; Breunig, Oliver; Bliesener, Andrea; Lippertz, Gertjan; Uday, Anjana; Taskin, A. A.; Loss, Daniel; Klinovaja, Jelena; Ando, Yoichi

doi:10.48550/arxiv.2109.05188

Cited by 4 publications

(7 citation statements)

References 7 publications

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“…nonreciprocal transport effect in bulk insulating nanowires provided strong evidence not only for quantum confinement of the surface states but also for the splitting of initially spindegenerate sub-bands that is predicted due to the breaking of inversion symmetry by a nonuniform potential through the cross-section of the nanowire [23]. This sub-band splitting is a key element required to achieve MBSs without a vortex [12].…”

Section: Introductionmentioning

confidence: 91%

“…In the past few years there has been substantial progress in the growth of thin TI nanowire devices [9,[13][14][15][16][17][18][19][20][21], including the growth of bulk insulating devices in which the chemical potential can be tuned close to the Dirac point [22,23]. In TI nanowires several transport signatures of the quantum confinement of surface states have been reported; previously these consisted of conductivity oscillations [24,25] as a function of magnetic field or gate voltage [13][14][15][16][17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Metallization and proximity superconductivity in topological insulator nanowires

Legg

Loss²,

Klinovaja³

2022

Phys. Rev. B

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A heterostructure consisting of a topological insulator (TI) nanowire brought into proximity with a superconducting layer provides a promising route to achieve topological superconductivity and associated Majorana bound states. Here we study the effects caused by such a coupling between a thin layer of an s-wave superconductor and a TI nanowire. We show that there is a distinct phenomenology arising from the metallization of states in the TI nanowire by the superconductor. In the strong coupling limit, required to induce a large superconducting pairing potential, we find that metallization results in a shift of the TI nanowire sub-bands (∼20 meV) as well as it leads to a small reduction in the size of the sub-band gap opened by a magnetic field applied parallel to the nanowire axis. Surprisingly, we find that metallization effects in TI nanowires can also be beneficial. Most notably, coupling to the superconductor induces a potential in the portion of the TI nanowire close to the interface with the superconductor; this breaks inversion symmetry and at finite momentum lifts the spin degeneracy of states within a sub-band. As such coupling to a superconductor can create or enhance the sub-band splitting that is key to achieving topological superconductivity. This is in stark contrast with semiconductors, where it has been shown that metallization effects always reduce the equivalent sub-band splitting caused by spin-orbit coupling. We also find that in certain geometries metallization effects can reduce the critical magnetic required to enter the topological phase. We conclude that, unlike in semiconductors, the metallization effects that occur in TI nanowires can be relatively easily mitigated, for instance, by modifying the geometry of the attached superconductor or by compensation of the TI material.

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Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Metallization and proximity superconductivity in topological insulator nanowires

Legg

Loss²,

Klinovaja³

2022

Phys. Rev. B

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“…The smallest coupling to charge noise occurs when the magnetic field is aligned to the well, where the effective Zeeman energy and the g-factor is widely tunable by external electric fields and by engineering the strain of the well. Strikingly, in an annular CQW, the maximal g-factor can reach rather large values, in analogy to topological insulator nanowires [41,42]. For this reason, CQWs can be effective architectures also in the search of exotic topological particles, such as Majorana fermions [43], where the low value of the g-factor along the hole nanowire is a critical issue [44].…”

Section: Introductionmentioning

confidence: 99%

Hole spin qubits in thin curved quantum wells

Bosco¹,

Loss²

2022

Preprint

Self Cite

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Hole spin qubits are frontrunner platforms for scalable quantum computers because of their large spin-orbit interaction which enables ultrafast all-electric qubit control at low power. The fastest spin qubits to date are defined in long quantum dots with two tight confinement directions, when the driving field is aligned to the smooth direction. However, in these systems the lifetime of the qubit is strongly limited by charge noise, a major issue in hole qubits. We propose here a different, scalable qubit design, compatible with planar CMOS technology, where the hole is confined in a curved germanium quantum well surrounded by silicon. This design takes full advantage of the strong spin-orbit interaction of holes, and at the same time suppresses charge noise in a wide range of configurations, enabling highly coherent, ultrafast qubit gates. While here we focus on a Si/Ge/Si curved quantum well, our design is also applicable to different semiconductors. Strikingly, these devices allow for ultrafast operations even in short quantum dots by a transversal electric field. This additional driving mechanism relaxes the demanding design constraints, and opens up a new way to reliably interface spin qubits in a single quantum dot to microwave photons. By considering stateof-the-art high-impedance resonators and realistic qubit designs, we estimate interaction strengths of a few hundreds of MHz, largely exceeding the decay rate of spins and photons. Reaching such a strong coupling regime in hole spin qubits will be a significant step towards high-fidelity entangling operations between distant qubits, as well as fast single-shot readout, and will pave the way towards the implementation of a large-scale semiconducting quantum processor.

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“…In the past few years there has been substantial progress in the growth of thin TI nanowire devices [9,[13][14][15][16][17][18][19][20][21], including the growth of bulk insulating devices in which the chemical potential can be tuned close to the Dirac point [22,23]. In TI nanowires several transport signatures of the quantum confinement of surface states have been reported, previously these consisted of conductivity oscillations [24,25] as a function of magnetic field or gate voltage [13][14][15][16][17][18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

“…In TI nanowires several transport signatures of the quantum confinement of surface states have been reported, previously these consisted of conductivity oscillations [24,25] as a function of magnetic field or gate voltage [13][14][15][16][17][18][19][20][21][22]. Recently, a non-reciprocal transport effect in bulk insulating nanowires provided strong evidence not only for quantum confinement of the surface states but also for the splitting of initially spindegenerate subbands that is predicted due to the breaking of inversion symmetry by a non-uniform potential through the cross-section of the nanowire [23]. This subband-splitting is a key element required to achieve MBSs without a vortex [12].…”

Section: Introductionmentioning

confidence: 99%

Metallization and proximity superconductivity in topological insulator nanowires

Legg,

Loss,

Klinovaja

2022

Preprint

Self Cite

View full text Add to dashboard Cite

A heterostructure consisting of a topological insulator (TI) nanowire brought into proximity with a superconducting layer provides a promising route to achieve topological superconductivity and associated Majorana bound states (MBSs). Here, we study effects caused by such a coupling between a thin layer of an s-wave superconductor and a TI nanowire. We show that there is a distinct phenomenology arising from the metallization of states in the TI nanowire by the superconductor. In the strong coupling limit, required to induce a large superconducting pairing potential, we find that metallization results in a shift of the TI nanowire subbands (∼ 20 meV) as well as it leads to a small reduction in the size of the subband gap opened by a magnetic field applied parallel to the nanowire axis. Surprisingly, we find that metallization effects in TI nanowires can also be beneficial. Most notably, coupling to the superconductor induces a potential in the portion of the TI nanowire close to the interface with the superconductor, this breaks inversion symmetry and at finite momentum lifts the spin degeneracy of states within a subband. As such coupling to a superconductor can create or enhance the subband splitting that is key to achieving topological superconductivity. This is in stark contrast to semiconductors, where it has been shown that metallization effects always reduce the equivalent subband-splitting caused by spin-orbit coupling. We also find that in certain geometries metallization effects can reduce the critical magnetic required to enter the topological phase. We conclude that, unlike in semiconductors, the metallization effects that occur in TI nanowires can be relatively easily mitigated, for instance by modifying the geometry of the attached superconductor or by compensation of the TI material.

show abstract

Giant magnetochiral anisotropy from quantum confined surface states of topological insulator nanowires

Cited by 4 publications

References 7 publications

Metallization and proximity superconductivity in topological insulator nanowires

Metallization and proximity superconductivity in topological insulator nanowires

Hole spin qubits in thin curved quantum wells

Metallization and proximity superconductivity in topological insulator nanowires

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