DARK MATTER researchers could be on the verge of cracking the cosmic mystery, thanks to a revolutionary device that will “listen” for dark matter particles.
Semiconductors are the basic building blocks of today’s digital, electronic age, providing us a multitude of devices that benefit our modern life, including computer, smartphones and other mobile devices. Improvements in semiconductor functionality and performance are likewise enabling next-generation applications of semiconductors for computing, sensing and energy conversion. Yet researchers have long struggled with limitations in our ability to fully understand the electronic charges inside semiconductor devices and advanced semiconductor materials, limiting our ability to drive further advances.
In a new study in the journal Nature, an IBM Research-led collaboration describes an exciting breakthrough in a 140-year-old mystery in physics—one that enables us to unlock the physical characteristics of semiconductors in much greater detail and aid in the development of new and improved semiconductor materials.
To truly understand the physics of semiconductors, we first need to know the fundamental properties of the charge carriers inside the materials, whether those particles are positive or negative, their speed under an applied electric field and how densely they are packed in the material. Physicist Edwin Hall found a way to determine those properties in 1879, when he discovered that a magnetic field will deflect the movement of electronic charges inside a conductor and that the amount of deflection can be measured as a voltage perpendicular to the flow of charge as shown in Fig. 1a. This voltage, known as the Hall voltage, unlocks essential information about the charge carriers in a semiconductor, including whether they are negative electrons or positive quasi-particles called “holes,” how fast they move in an electric field or their “mobility” (µ) and their density (n) inside the semiconductor.
CERN’s colossal complex of accelerators is in the midst of a two-year shutdown for upgrade work. But that doesn’t mean all experiments at the Laboratory have ceased to operate. The CLOUD experiment, for example, has just started a data run that will last until the end of November.
The CLOUD experiment studies how ions produced by high-energy particles called cosmic rays affect aerosol particles, clouds and the climate. It uses a special cloud chamber and a beam of particles from the Proton Synchrotron to provide an artificial source of cosmic rays. For this run, however, the cosmic rays are instead natural high-energy particles from cosmic objects such as exploding stars.
“Cosmic rays, whether natural or artificial, leave a trail of ions in the chamber,” explains CLOUD spokesperson Jasper Kirkby, “but the Proton Synchrotron provides cosmic rays that can be adjusted over the full range of ionisation rates occurring in the troposphere, which comprises the lowest ten kilometres of the atmosphere. That said, we can also make progress with the steady flux of natural cosmic rays that make it into our chamber, and this is what we’re doing now.”
Circa 2010
Ultra-fast pulses from a powerful laser can create droplets of water out of thin air, according to a new study. With the right conditions and large enough droplets, the researchers say, the technique could be used to make rain on demand.
Rain forms when water condenses around tiny particles in the atmosphere. Most of the time, dust or pollen do the job, but humans have long attempted to speed the process by seeding clouds with chemicals like silver iodide. Those chemicals provide the so-called “condensation nuclei” that trigger the consolidation of water into raindrops.
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Scientists have observed a quantum vibration at normal room temperature for the first time, a phenomenon that usually requires ultra-cold, carefully calibrated conditions – bringing us another step closer to understanding the behaviour of quantum mechanics in common materials.
The team was able to spot a phonon, a quantum particle of vibration generated from high-frequency laser pulses, in a piece of diamond. These phonons are notoriously hard to detect, partly because of their sensitivity to heat.
What makes observing a phonon so important is that it shows a vibration acting as a single unit of energy (as described by quantum mechanics), as well as a wave (as described by classical physics). At room temperature in open air conditions, it brings quantum behaviour “closer to our daily life” in the words of the researchers.
Dive into the subatomic world, into the heart of protons or neutrons, and you’ll find elementary particles known as quarks. Measuring the mass of these quarks can be challenging, but new results from the CMS collaboration reveal for the first time how the mass of the top quark – the heaviest of six types of quarks – varies depending on the energy scale used to measure the particle.
The theory of quantum chromodynamics, a component of the Standard Model, predicts this energy-scale variation, known as running, for the masses of all quarks and for the strong force acting between them. Observing the running masses of quarks can therefore provide a way of testing quantum chromodynamics and the Standard Model.
Experiments at CERN and other laboratories have already measured the running masses of the bottom and charm quarks, the second and third heaviest quarks, and the results were in agreement with quantum chromodynamics. Now, the CMS collaboration has used data from high-energy proton–proton collisions at the Large Hadron Collider to chase out the running mass of the top quark.
Dark matter, which researchers believe make up about 80% of the universe’s mass, is one of the most elusive mysteries in modern physics. What exactly it is and how it came to be is a mystery, but a new Johns Hopkins University study now suggests that dark matter may have existed before the Big Bang.
The study, published August 7 in Physical Review Letters, presents a new idea of how dark matter was born and how to identify it with astronomical observations.
“The study revealed a new connection between particle physics and astronomy. If dark matter consists of new particles that were born before the Big Bang, they affect the way galaxies are distributed in the sky in a unique way. This connection may be used to reveal their identity and make conclusions about the times before the Big Bang too,” says Tommi Tenkanen, a postdoctoral fellow in Physics and Astronomy at the Johns Hopkins University and the study’s author.
One of the fundamental challenges of physics is the reconciliation of Einstein’s theory of relativity and quantum mechanics. The necessity to critically question these two pillars of modern physics arises, for example, from extremely high-energy events in the cosmos, which so far can only ever be explained by one theory at a time, but not both theories in harmony. Researchers around the world are therefore searching for deviations from the laws of quantum mechanics and relativity that could open up insights into a new field of physics.
For a recent publication, scientists from Leibniz University Hannover and Ulm University have taken on the twin paradox known from Einstein’s special theory of relativity. This thought experiment revolves around a pair of twins: While one brother travels into space, the other remains on Earth. Consequently, for a certain period of time, the twins are moving in different orbits in space. The result when the pair meets again is quite astounding: The twin who has been travelling through space has aged much less than his brother who stayed at home. This phenomenon is explained by Einstein’s description of time dilation: Depending on the speed and where in the gravitational field two clocks move relative to each other, they tick at different speeds.
For the publication in Science Advances, the authors assumed a quantum-mechanical variant of the twin paradox with only one twin. Thanks to the superposition principle of quantum mechanics, this twin can move along two paths at the same time. In the researchers’ thought experiment, the twin is represented by an atomic clock. “Such clocks use the quantum properties of atoms to measure time with high precision. The atomic clock itself is therefore a quantum-mechanical object and can move through space-time on two paths simultaneously due to the superposition principle. Together with colleagues from Hannover, we have investigated how this situation can be realised in an experiment,” explains Dr. Enno Giese, research assistant at the Institute of Quantum Physics in Ulm. To this end, the researchers have developed an experimental setup for this scenario on the basis of a quantum-physical model.
The standard model of physics remains incomplete. Could supersymmetry fill the gaps? From whether supersymmetric particles could fix the mass of the Higgs Boson to what this would mean for string theory, the world’s leading thinkers explain all.
John Ellis is a British theoretical physicist who is currently Clerk Maxwell Professor of Theoretical Physics at King’s College London. He was Division Leader for the CERN theory division, a founding member of the LEPC and of the LHCC at CERN and currently chair of the committee to investigate physics opportunities for future proton accelerators.
