Noise and current correlations in tunnel junctions of quantum spin Hall edge states

Dolcini, Fabrizio

doi:10.1103/physrevb.92.155421

Cited by 16 publications

(9 citation statements)

References 47 publications

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“…Further, while local shot noise correlations have been calculated in some recent works with QSH samples 19 to our knowledge this is the first work wherein both the non-local charge and spin shot noise correlations have been used as a probe of helicity and its topological origins and also to discriminate between chiral and helical edge modes. In 1950, R Hanbury Brown and R Twiss found out the diameter of radio stars via a intensity-intensity correlation experiment 8 , 28 .…”

Section: Introductionmentioning

confidence: 99%

“…Further these studies are in presence of a QPC in a QSH bar, as in refs 16 – 18 . There are also few papers on current-current correlation studied via the scattering matrix approach or other than helical Luttinger liquid approach, see refs 19 and 20 . In ref.…”

Section: Introductionmentioning

confidence: 99%

“…There are also few papers on current-current correlation studied via the scattering matrix approach or other than helical Luttinger liquid approach, see Refs. 19,20 . In Ref.…”

Section: Introductionmentioning

confidence: 99%

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Probing helicity and the topological origins of helicity via non-local Hanbury-Brown and Twiss correlations

Mani

Benjamin

2017

Sci Rep

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Quantum Hall edge modes are chiral while quantum spin Hall edge modes are helical. However, unlike chiral edge modes which always occur in topological systems, quasi-helical edge modes may arise in a trivial insulator too. These trivial quasi-helical edge modes are not topologically protected and therefore need to be distinguished from helical edge modes arising due to topological reasons. Earlier conductance measurements were used to identify these helical states, in this work we report on the advantage of using the non local shot noise as a probe for the helical nature of these states as also their topological or otherwise origin and compare them with chiral quantum Hall states. We see that in similar set-ups affected by same degree of disorder and inelastic scattering, non local shot noise “HBT” correlations can be positive for helical edge modes but are always negative for the chiral quantum Hall edge modes. Further, while trivial quasi-helical edge modes exhibit negative non-local”HBT” charge correlations, topological helical edge modes can show positive non-local “HBT” charge correlation. We also study the non-local spin correlations and Fano factor for clues as regards both the distinction between chirality/helicity as well as the topological/trivial dichotomy for helical edge modes.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Probing helicity and the topological origins of helicity via non-local Hanbury-Brown and Twiss correlations

Mani

Benjamin

2017

Sci Rep

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“…A natural continuation to the measurements of average current is to measure correlations in it, i.e., noise. Theoretical studies of noise in 2D TIs have focused on point-contacts and more complicated geometries [38][39][40][41][42][43]. The simpler case of two-terminal noise of a long single edge has been measured only recently [44].…”

Section: Introductionmentioning

confidence: 99%

Current Noise from a Magnetic Moment in a Helical Edge

Väyrynen

Glazman

2017

Phys. Rev. Lett.

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We calculate the two-terminal current noise generated by a magnetic moment coupled to a helical edge of a two-dimensional topological insulator. When the system is symmetric with respect to in-plane spin rotation, the noise is dominated by the Nyquist component even in the presence of a voltage bias V . The corresponding noise spectrum S(V, ω) is determined by a modified fluctuationdissipation theorem with the differential conductance G(V, ω) in place of the linear one. The differential noise ∂S/∂V , commonly measured in experiments, is strongly dependent on frequency on a small scale τ −1 KT set by the Korringa relaxation rate of the local moment. This is in stark contrast with the case of conventional mesoscopic conductors where ∂S/∂V is frequency-independent and defined by the shot noise. In a helical edge, a violation of the spin-rotation symmetry leads to the shot noise, which becomes important only at a high bias. Uncharacteristically for a fermion system, this noise in the backscattered current is super-Poissonian. Introduction.The edge conduction [1][2][3][4][5][6][7] in twodimensional topological insulators [8][9][10][11] (2D TI) such as HgTe and InAs/GaSb still poses unresolved questions. The lack of topological protection [1-3, 12-15] of the modes in both materials and the edge conductance in InAs/GaSb structures having similar values in the trivial and topological phases [16,17], are not understood. The former question has created a plethora of theoretical activity in trying to identify the relevant time-reversal symmetric backscattering mechanism [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. Charge puddles, ubiquitous in narrow-gap semiconductors and capable of having a magnetic moment, are a plausible candidate to explain the phenomena [35,36] and may have been observed in local measurements [37].

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“…We instead target a still open question, namely how helical edge states interact with each other.A quantum point contact (QPC) can be used to guide * All three authors contributed equally to this work, email: Jonas.Strunz@physik.uni-wuerzburg.de edge channels from opposite boundaries of the sample into a constriction. Such a device allows for studies of charge and spin transfer mechanisms by, e.g., adjusting the overlap of the edge states [11][12][13][14][15][16][17][18][19][20]. Besides the general interest in the study of transport processes in such a device, the appropriate model to describe the essential physics and to capture interaction effects of helical edge states is still unclear.…”

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confidence: 99%

Interacting topological edge channels

et al. 2019

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Electrical currents in a quantum spin Hall insulator are confined to the boundary of the system. The charge carriers can be described as massless relativistic particles, whose spin and momentum are coupled to each other. While the helical character of those states is by now well established experimentally, it is a fundamental open question how those edge states interact with each other when brought in spatial proximity. We employ a topological quantum point contact to guide edge channels from opposite sides into a quasi-onedimensional constriction, based on inverted HgTe quantum wells. Apart from the expected quantization in integer steps of 2e 2 /h, we find a surprising additional plateau at e 2 /h. We explain our observation by combining band structure calculations and repulsive electron-electron interaction effects captured within the Tomonaga-Luttinger liquid model. The present results may have direct implications for the study of one-dimensional helical electron quantum optics, Majorana-and potentially para-fermions. The quantum spin Hall effect has been predicted in several systems [1][2][3][4] and was first realized in HgCdTe/HgTe quantum wells [5]. Later, this phase was observed in other material systems such as InAs/GaSb double quantum wells [6] and in monolayers of WTe 2 and bismuthene [7,8]. The defining properties of this state, related to its helical nature, are well established by numerous experiments such as the observation of conductance quantization of two spin polarized edge channels G 0 = 2e 2 /h with e the electron charge and h the Planck's constant [5]. Additionally, non-local edge transport and spin-polarization of the edge channels were demonstrated by suitable transport experiments [9,10]. We instead target a still open question, namely how helical edge states interact with each other.A quantum point contact (QPC) can be used to guide * All three authors contributed equally to this work, email: Jonas.Strunz@physik.uni-wuerzburg.de edge channels from opposite boundaries of the sample into a constriction. Such a device allows for studies of charge and spin transfer mechanisms by, e.g., adjusting the overlap of the edge states [11][12][13][14][15][16][17][18][19][20]. Besides the general interest in the study of transport processes in such a device, the appropriate model to describe the essential physics and to capture interaction effects of helical edge states is still unclear. The one-dimensionality of the helical edge modes suggests a description in terms of the Tomonaga-Luttinger liquid when electron-electron interactions are taken into account. In this respect, the QPC setup provides an illuminating platform as it may give rise to particular backscattering processes.We present the realization of a QPC based on HgTe quantum wells as evidenced by the observation of the expected conductance steps in integer values of G 0 . The newly developed lithographic process allows the fabrication of sophisticated nanostructures based on topological materials without lowering the material quality. It t...

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Noise and current correlations in tunnel junctions of quantum spin Hall edge states

Cited by 16 publications

References 47 publications

Probing helicity and the topological origins of helicity via non-local Hanbury-Brown and Twiss correlations

Probing helicity and the topological origins of helicity via non-local Hanbury-Brown and Twiss correlations

Current Noise from a Magnetic Moment in a Helical Edge

Interacting topological edge channels

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