Flux Quantization Effects in InN Nanowires

Abstract

InN nanowires, grown by plasma-enhanced molecular beam epitaxy, were investigated by means of magnetotransport. By performing temperature-dependent transport measurements and current measurements on a large number of nanowires of different dimensions, it is proven that the carrier transport mainly takes place in a tube-like surface electron gas. Measurements on three representative nanowires under an axially oriented magnetic field revealed pronounced magnetoconductance oscillations with a periodicity corresponding to a single magnetic flux quantum. The periodicity is explained by the effect of the magnetic flux penetrating the coherent circular quantum states in the InN nanowires, rather than by Aharonov-Bohm type interferences. The occurrence of the single magnetic flux quantum periodicity is attributed to the magnetic flux dependence of phase-coherent circular states with different angular momentum quantum numbers forming the one-dimensional transport channels. These phase coherent states can exist because of the almost ideal crystalline properties of the InN nanowires prepared by self-assembled growth.

Topological Insulator Materials

“…134,135) Such an observation suggests the existence of some surface conduction layer, but its topological nature is still left to be confirmed, because similar AB oscillations are known to originate from trivial surface states in InN nanowires. 136) A very interesting candidate is SmB 6 , which may be a topological Kondo insulator, [137][138][139] because the band bap of this material stems from Kondo effect. If this material is indeed a TI, it will be the first material where electron correlations and nontrivial band topology both play important roles.…”

Conductance oscillations of core-shell nanowires in transversal magnetic fields

“…Most commonly CSNs have hexagonal cross-sections [6][7][8], but triangular [9,10] and circular [11] systems have also been achieved. Electrons confined in prismatic CSNs may form conductive channels along the sharp edges [2,[12][13][14][15][16][17].…”

Spin-orbit coupling and phase-coherent transport in InN nanowires

“…Semiconductor nanowires fabricated by a bottom-up approach are not only interesting for the realization of future nanoscaled devices 1,2 but also appear to be very attractive model systems to tackle fundamental questions concerning the transport in strongly confined systems. [3][4][5] In order to avoid the problem connected with carrier depletion, narrowband gap semiconductors, i.e., InAs or InN, 1,6,7 are preferred. The underlying reason is that here the Fermi-level pinning in the conduction band results in a carrier accumulation at the surface.…”

“…In fact, the tubular topology of the surface electron gas opens up the possibility to observe unconventional quantum transport phenomena. 7 When the phase-coherence length l in the nanowire is comparable to its dimensions the conductance fluctuates if a magnetic field is applied or if the electron concentration is changed by means of a gate electrode. [8][9][10] These so-called universal conductance fluctuations being in the order of e 2 / h originate from the fact that in small disordered samples, electron interference effects are not averaged out.…”

“…26 We estimated the theoretically expected Rashba coupling parameter ␣ by assuming that the electrons are located predominantly in a surface two-dimensional electron gas ͑2DEG͒. 7 The wave function and potential profile of a cylindrical 2DEG required for the calculation of the Rashba coupling parameter 27 was gained from a Schrödinger-Poisson solver. In contrast to the value resulting from the fit to the Kettemann model, we obtained considerably smaller value of 0.6ϫ 10 −12 eV m for ␣ R .…”