Terahertz Magnetospectroscopy of Cyclotron Resonances from Topological Surface States in Thick Films of Cd_xHg_1−xTe

Abstract

Herein, studies of the cyclotron resonance (CR) in thick films with different cadmium contents corresponding to materials with and without band inversion, as well as critical content corresponding to an almost linear energy dispersion are presented. The results demonstrate that the formation of 2D topological surface states requires sharp interfaces between layers with and without band inversion, in which case the corresponding CR is clearly observed for the out‐of‐plane orientation of magnetic field but does not show up for an in‐plane orientation. In contrast, all samples having more conventional technological design with smooth interfaces (i.e., containing regions of with gradually changing Cd content x) show equally pronounced CR in both in‐plane and out‐of‐plane magnetic field revealing that CR is excited in effectively 3D states. Modeling of the surface states for different film designs supports main observations. In all samples, additional broad helicity‐independent resonances are observed, which are attributed to photoionization and magnetic freeze‐out of impurity states.

Transport properties of a 1000 nm HgTe film: the interplay of surface and bulk carriers

“…The latter have the same origin as the TSSs [18,19], but they form only if there is a smooth transition between topologically trivial and non-trivial materials or if there is strong enough band bending near the boundary of materials with the opposite topology [19]. We expect to have a sharp interface between HgTe and CdHgTe barriers since it can be controlled well during the epitaxy growth [15], and suggest the band bending induced by the gate creates conditions for the VPS formation. For our study, the difference between VPS and bulk electrons in the accumulation layer is immaterial.…”

“…However, apart from magneto-optic measurements [11][12][13][14][15] and a short transport report [8], there has been no systematic study of transport properties of bulk HgTe where TSSs are taken into account. Compared to previously studied 80and 200 nm HgTe films, a much thicker 1000 nm film has trivial bulk three-dimensional (3D) carriers that can interact with TSSs and modify their transport response.…”

Transport properties of a 1000-nm HgTe film: the interplay of surface and bulk carriers

“…The latter have the same origin as the topological surface states [18,19], but they form only if there is a smooth transition between topologically trivial and non-trivial ( T ) materials, or if there is strong enough band bending near the boundary of materials with the opposite topology [19]. We expect to have a sharp interface between HgTe and CdHgTe barriers since it can be controlled well during the epitaxy growth [15], and suggest the induced by the gate band bending creates conditions for the VPS formation. For our study, the difference between VPS and bulk electrons in the accumulation layer is immaterial.…”

“…However, apart from magneto-optic measurements [11][12][13][14][15] and a short transport report [8], there * mlsavchenko@isp.nsc.ru was no systematic study of transport properties of bulk HgTe, where topological surface states are taking into account. Compare to previously studied 80-and 200-nm HgTe films, a much thicker 1000-nm film has trivial bulk 3D carriers that can interact with topological surface states and modify their transport response.…”

Исследования фоточувствительности узкозонных и бесщелевых твердых растворов HgCdTe в терагерцовом и субтерагерцовом диапазоне частот

“…Хорошо известно, что при x c ∼ 0.168 в твердом растворе Hg 1−x Cd x Te происходит инверсия зон, в результате чего при x < x c твердый раствор является полуметаллом с нулевой энергетической щелью между состояниями валентной зоны и зоны проводимости [6]. Инвертированный порядок зон в таких полуметаллах сопряжен с появлением топологических состояний на границе образца, обладающих уникальными свойствами, что обусловливает большое количество работ, посвященных их исследованию разнообразными методами [3,[7][8][9].…”