Time-reversal symmetry breaking versus superstructure

One of the mysteries of modern condenced-matter physics is the nature of the pseudogap state of the superconducting cuprates. Kaminski et al.1 claimed to have observed signatures of time-reversal symmetry breaking in the pseudogap regime in underdoped Bi2Sr2CaCu2O8+d (Bi2212). Here we argue that the observed dichroism is due to the 5x1 superstructure replica of the electronic bands and therefore cannot be considered as evidence for the spontaneous time-reversal symmetry breaking in cuprates.Comment: 5 pages, pd

Colloidal PbS nanoplatelets synthesized via cation exchange for electronic applications

In this work, we present a new synthetic approach to colloidal PbS nanoplatelets (NPLs) utilizing a cation exchange (CE) strategy starting from CuS NPLs synthesized via the hot-injection method. Whereas the thickness of the resulting CuS NPLs was fixed at approx. 5 nm, the lateral size could be tuned by varying the reaction conditions, such as time from 6 to 16 h, the reaction temperature (120 °C, 140 °C), and the amount of copper precursor. In a second step, Cu+ cations were replaced with Pb2+ ions within the crystal lattice via CE. While the shape and the size of parental CuS platelets were preserved, the crystal structure was rearranged from hexagonal covellite to PbS galena, accompanied by the fragmentation of the monocrystalline phase into polycrystalline one. Afterwards a halide mediated ligand exchange (LE) was carried out in order to remove insulating oleic acid residues from the PbS NPL surface and to form stable dispersions in polar organic solvents enabling thin-film fabrication. Both CE and LE processes were monitored by several characterization techniques. Furthermore, we measured the electrical conductivity of the resulting PbS NPL-based films before and after LE and compared the processing in ambient to inert atmosphere. Finally, we fabricated field-effect transistors with an on/off ratio of up to 60 and linear charge carrier mobility for holes of 0.02 cm2 V−1 s−1

Universal electronic structure of polar oxide hetero-interfaces

The electronic properties of NdGaO3/SrTiO3, LaGaO3/SrTiO3, and LaAlO3/SrTiO3 interfaces, all showing an insulator-to-metal transition as a function of the overlayer-thickness, are addressed in a comparative study based on x-ray absorption, x-ray photoemission and resonant photoemission spectroscopy. The nature of the charge carriers, their concentration and spatial distribution as well as the interface band alignments and the overall interface band diagrams are studied and quantitatively evaluated. The behavior of the three analyzed heterostructures is found to be remarkably similar. The valence band edge of all the three overlayers aligns to that of bulk SrTiO3. The near-interface SrTiO3 layer is affected, at increasing overlayer thickness, by the building-up of a confining potential. This potential bends both the valence and the conduction band downwards. The latter one crossing the Fermi energy in the proximity of the interface and determines the formation of an interfacial band offset growing as a function of thickness. Quite remarkably, but in agreement with previous reports for LaAlO3/SrTiO3, no electric field is detected inside any of the polar overlayers. The essential phenomenology emerging from our findings is discussed on the base of different alternative scenarios regarding the origin of interface carriers and their interaction with an intense photon beam

A virtual equipment as a test bench for evaluating virtual metrology algorithms

This paper presents a Virtual Equipment which serves as a testing environment for evaluating Virtual Metrology (VM) algorithms prior to their implementation into semiconductor fab structures. The Virtual Equipment merges statistical simulation with physical simulation to generate test data sets for various common and uncommon states of the processing equipment. The input data is based on history fab data and synthetically generated data. Main result of the presented work is the bidirectional link of statistical methods with physical simulations which is the core of the virtual test environment. The testing of VM algorithms can be controlled via a Graphical User Interface (GUI). A simplified physical simulation of a Chemical Vapor Deposition (CVD) reaction chamber is set up based on CAD dat a as an example of the physical simulation part

IMPROVE - a joint European effort to boost efficiency in semiconductor manufacturing: Presentation held at APC Conference XXIV 2012, 10.09.2012 to 12.09.2012, Ann Arbor, Michigan

Semiconductor devices are the essential basis for electronics-based value chains for, e.g., automotive, transport, energy efficiency, or medical technology. Those value chains are well-known strengths of European industry thus, it is of utmost importance to also keep the basis, i.e. semiconductor manufacturing in Europe. The research and development of manufacturing science solutions to substantially enhance efficiency was identified as competitiveness enabler for European semiconductor fabs

Low-temperature enhancement of ferromagnetic Kitaev correlations in alpha-RuCl3

Kitaev-type interactions between neighboring magnetic moments emerge in the honeycomb material alpha-RuCl3. It is debated, however, whether these Kitaev interactions are ferromagnetic or antiferromagnetic. With electron energy loss spectroscopy (EELS) we study the lowest excitation across the Mott-Hubbard gap, which involves a d(4) triplet in the final state and therefore is sensitive to nearest-neighbor spin-spin correlations. At low temperatures the spectral weight of these triplets is strongly enhanced, in accordance with optical data. We show that the magnetic correlation function that determines this EELS spectral weight is directly related to a Kitaev-type spin-spin correlator and that the temperature dependence agrees very well with the results of a microscopic magnetic Hamiltonian for alpha-RuCl3 with ferromagnetic Kitaev coupling