121 research outputs found
Margin trading and leverage management
We use granular data covering regulated (brokerage-financed) and unregulated (shadow-financed) margin trading during the 2015 market turmoil in China to provide the first systematic analysis of margin investors' characteristics, leverage management policies, and liquidation choices. We show that leverage constraints induced substantial forced and preemptive sales, and leverage and cash management differed substantially across investor and account types. We explore the relation between margin trading and shock propagation, and show that China's price limit rule led to unintended contagion across stocks. Compared to brokerage investors, shadow investors were closer to their leverage constraints, and played a more significant role in transmitting shocks across stocks
New fermions on the line in topological symmorphic metals
Topological metals and semimetals (TMs) have recently drawn significant
interest. These materials give rise to condensed matter realizations of many
important concepts in high-energy physics, leading to wide-ranging protected
properties in transport and spectroscopic experiments. The most studied TMs,
i.e., Weyl and Dirac semimetals, feature quasiparticles that are direct
analogues of the textbook elementary particles. Moreover, the TMs known so far
can be characterized based on the dimensionality of the band crossing. While
Weyl and Dirac semimetals feature zero-dimensional points, the band crossing of
nodal-line semimetals forms a one-dimensional closed loop. In this paper, we
identify a TM which breaks the above paradigms. Firstly, the TM features
triply-degenerate band crossing in a symmorphic lattice, hence realizing
emergent fermionic quasiparticles not present in quantum field theory.
Secondly, the band crossing is neither 0D nor 1D. Instead, it consists of two
isolated triply-degenerate nodes interconnected by multi-segments of lines with
two-fold degeneracy. We present materials candidates. We further show that
triplydegenerate band crossings in symmorphic crystals give rise to a Landau
level spectrum distinct from the known TMs, suggesting novel magneto-transport
responses. Our results open the door for realizing new topological phenomena
and fermions including transport anomalies and spectroscopic responses in
metallic crystals with nontrivial topology beyond the Weyl/Dirac paradigm.Comment: 24 pages, 4 figures, and 1 tabl
Gapped Electronic Structure of Epitaxial Stanene on InSb(111)
Stanene (single-layer grey tin), with an electronic structure akin to that of
graphene but exhibiting a much larger spin-orbit gap, offers a promising
platform for room-temperature electronics based on the quantum spin Hall (QSH)
effect. This material has received much theoretical attention, but a suitable
substrate for stanene growth that results in an overall gapped electronic
structure has been elusive; a sizable gap is necessary for room-temperature
applications. Here, we report a study of stanene epitaxially grown on the
(111)B-face of indium antimonide (InSb). Angle-resolved photoemission
spectroscopy (ARPES) measurements reveal a gap of 0.44 eV, in agreement with
our first-principles calculations. The results indicate that stanene on
InSb(111) is a strong contender for electronic QSH applications.Comment: 15 pages, 4 figure
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