Type I superconductivity in the Dirac semimetal PdTe2

The superconductor PdTe$_2$ was recently classified as a Type II Dirac semimetal, and advocated to be an improved platform for topological superconductivity. Here we report magnetic and transport measurements conducted to determine the nature of the superconducting phase. Surprisingly, we find that PdTe$_2$ is a Type I superconductor with $T_c = 1.64$ K and a critical field $\mu_0 H_c (0) = 13.6$ mT. Our crystals also exhibit the intermediate state as demonstrated by the differential paramagnetic effect. For $H > H_c$ we observe superconductivity of the surface sheath. This calls for a close examination of superconductivity in PdTe$_2$ in view of the presence of topological surface states.Comment: 5 page

The impact of Group Intelligence software on enquiry-based learning

Despite the increasing use of groupware technologies in education, there is little evidence of their impact, especially within an enquiry-based learning (EBL) context. In this paper, we examine the use of a commercial standard Group Intelligence software called GroupSystems®ThinkTank. To date, ThinkTank has been adopted mainly in the USA and supports teams in generating ideas, categorising, prioritising, voting and multi-criteria decision-making and automatically generates a report at the end of each session. The software was used by students carrying out an EBL project, set by employers, for a full academic year. The criteria for assessing the impact of ThinkTank on student learning were those of creativity, participation, productivity, engagement and understanding. Data was collected throughout the year using a combination of interviews and questionnaires, and written feedback from employers. The overall findings show an increase in levels of productivity and creativity, evidence of a deeper understanding of their work but some variation in attitudes towards participation in the early stages of the project

Superconductivity under pressure in the Dirac semimetal PdTe2

The Dirac semimetal PdTe$_2$ was recently reported to be a type-I superconductor ($T_c =$1.64 K, $\mu_0 H_c (0) = 13.6$ mT) with unusual superconductivity of the surface sheath. We here report a high-pressure study, $p \leq 2.5$ GPa, of the superconducting phase diagram extracted from ac-susceptibility and transport measurements on single crystalline samples. $T_c (p)$ shows a pronounced non-monotonous variation with a maximum $T_c =$1.91 K around 0.91 GPa, followed by a gradual decrease to 1.27 K at 2.5 GPa. The critical field of bulk superconductivity in the limit $T \rightarrow 0$, $H_c(0,p)$, follows a similar trend and consequently the $H_c(T,p)$-curves under pressure collapse on a single curve: $H_c(T,p)=H_c(0,p)[1-(T/T_c(p))^2]$. Surface superconductivity is robust under pressure as demonstrated by the large superconducting screening signal that persists for applied dc-fields $H_a > H_c$. Surprisingly, for $p \geq 1.41$ GPa the superconducting transition temperature at the surface $T_c^S$ is larger than $T_c$ of the bulk. Therefore surface superconductivity may possibly have a non-trivial nature and is connected to the topological surface states detected by ARPES. We compare the measured pressure variation of $T_c$ with recent results from band structure calculations and discuss the importance of a Van Hove singularity.Comment: manuscript 9 pages with 8 figures + supplemental material 3 pages with 6 figure

Electric‐field dependence of interband transitions in In_(0.53)Ga_(0.47)As/In_(0.52)Al_(0.48)As single quantum wells by room‐temperature electrotransmittance

Room‐temperature electrotransmittance has been used in order to investigate the interband excitonic transitions in a 250‐Å‐thick In_(0.53)Ga_(0.47)As/In_(0.52)Al_(0.48)As single‐quantum‐well system as a function of an externally applied electric field. Parity forbidden transitions, involving conduction‐band states with quantum numbers up to n=5, which become more pronounced at high electric fields were observed. The ground‐state and the forbidden transitions showed a significant red shift due to the quantum confined Stark effect. A comparison with previously reported results on thinner InGaAs/InAlAs quantum wells indicated that the wide‐well sample exhibits the largest shift, as expected from theory. Despite the appreciable Stark shift, the rather large, field‐induced linewidth broadening and the relatively low electric field at which the ground‐state exciton is ionized poses limitations on using this wide‐quantum‐well system for electro‐optic applications

Spiking neurons with short-term synaptic plasticity form superior generative networks

Spiking networks that perform probabilistic inference have been proposed both as models of cortical computation and as candidates for solving problems in machine learning. However, the evidence for spike-based computation being in any way superior to non-spiking alternatives remains scarce. We propose that short-term plasticity can provide spiking networks with distinct computational advantages compared to their classical counterparts. In this work, we use networks of leaky integrate-and-fire neurons that are trained to perform both discriminative and generative tasks in their forward and backward information processing paths, respectively. During training, the energy landscape associated with their dynamics becomes highly diverse, with deep attractor basins separated by high barriers. Classical algorithms solve this problem by employing various tempering techniques, which are both computationally demanding and require global state updates. We demonstrate how similar results can be achieved in spiking networks endowed with local short-term synaptic plasticity. Additionally, we discuss how these networks can even outperform tempering-based approaches when the training data is imbalanced. We thereby show how biologically inspired, local, spike-triggered synaptic dynamics based simply on a limited pool of synaptic resources can allow spiking networks to outperform their non-spiking relatives.Comment: corrected typo in abstrac

Tip-enhanced strong coupling spectroscopy, imaging, and control of a single quantum emitter

Optical cavities can enhance and control light-matter interactions. This level of control has recently been extended to the nanoscale with single emitter strong coupling even at room temperature using plasmonic nanostructures. However, emitters in static geometries, limit the ability to tune the coupling strength or to couple different emitters to the same cavity. Here, we present tip-enhanced strong coupling (TESC) with a nanocavity formed between a scanning plasmonic antenna tip and the substrate. By reversibly and dynamically addressing single quantum dots, we observe mode splitting up to 160 meV and anticrossing over a detuning range of ~100 meV, and with subnanometer precision over the deep subdiffraction-limited mode volume. Thus, TESC enables previously inaccessible control over emitter-nanocavity coupling and mode volume based on near-field microscopy. This opens pathways to induce, probe, and control single-emitter plasmon hybrid quantum states for applications from optoelectronics to quantum information science at room temperature

Muon spin rotation study of the topological superconductor SrxBi2Se3

We report transverse-field (TF) muon spin rotation experiments on single crystals of the topological superconductor Sr$_x$Bi$_2$Se$_3$ with nominal concentrations $x=0.15$ and $0.18$ ($T_c \sim 3$ K). The TF spectra ($B= 10$ mT), measured after cooling to below $T_c$ in field, did not show any additional damping of the muon precession signal due to the flux line lattice within the experimental uncertainty. This puts a lower bound on the magnetic penetration depth $\lambda \geq 2.3 ~\mu$m. However, when we induce disorder in the vortex lattice by changing the magnetic field below $T_c$ a sizeable damping rate is obtained for $T \rightarrow 0$. The data provide microscopic evidence for a superconducting volume fraction of $\sim 70~ \%$ in the $x=0.18$ crystal and thus bulk superconductivity.Comment: 6 pages, includes 4 figure

Financial Technologies: a Note on Mobile Payment

The financial market is currently disrupted by the rise of new technologies "FinTech” a short form for financial technology, which profoundly reshapes the financial intermediary structure and makes financial services more efficient. Mobile technology with Internet-enabled devices are the next logical phase of the World Wide Web campaign such as mobile phone taking over the mass market and will fundamentally change the way products are buy and sell as well as financial services especially the mobile payment system. This research examines changes payment method in financial services, particularly those involving mobile payments that can create new channels for consumers to purchase goods and services using mobile phone. Mobile payment application is ready to replace traditional cash, checks, credit and debit card throughout the country. In this stage of development, the current situation of mobile payment market, review the previous literature on mobile payment services, analysis use of mobile payment worldwide and various initiatives use mobile phones to offer financial services for those ‘unbanked\u27