A Daily Dose of Physics
Physics is the foundation for understanding the natural world, from the smallest particles to the complex behavior of materials and devices. In this section, I share explanations of concepts from theoretical and experimental physics that I have studied, researched, or find fascinating. The goal of this series is to make physics more approachable by exploring fundamental ideas, scientific discoveries, and the connections between theory and experiment. The topics cover areas such as condensed matter physics, quantum materials, and modern physics.
Let's learn some concepts in physics
Learn about Hall effect and it's signature in superconducting materials.
What is the limit of resistance one can measure?
How do you know how low the resistance is once the material goes through the phase transition to superconductivity state? and what do we mean by zero resistance?
Life of an experimental physicist
Physics is not only about developing theories and mathematical models; it is also about designing experiments and building the tools that allow us to explore the physical world. Experimental physicists use advanced fabrication techniques and measurement systems to create, manipulate, and understand materials and devices.
Throughout my research journey, I have worked with a wide range of experimental techniques used in condensed matter physics, quantum materials, and semiconductor device research. These techniques include thin film growth, nanofabrication, cleanroom processing, and advanced material characterization.
In this section, I introduce the fundamental principles behind the experimental tools used to fabricate and study modern materials and nanoscale devices.
Experimental Tools:
Experimental physics relies on the ability to observe, measure, and manipulate physical systems. To investigate the properties of materials, experimental physicists use a wide range of specialized instruments that allow them to probe structural, electronic, magnetic, and optical behaviors at different length scales. Throughout my research journey, I have worked with various fabrication and characterization tools used to study advanced materials and nanoscale devices. In this section, I introduce the fundamental principles behind these techniques, explain how the instruments operate, and discuss their applications in modern physics research. The topics covered include thin-film deposition techniques, nanofabrication methods, microscopy, spectroscopy, and electrical characterization tools.
Physical Property Measurement System (PPMS)
One of the essential measurements in a physics lab is a transport properties like measuring resistivity, Ac Susceptibility, Hall effect, and other kind of transport properties. The Physical Property Measurement System or PPMS for short is the device which makes these kind of experiment happen. The cool thing about PPMS or device like that is the possibility of measuring the transport properties of all kind of material at very low temperature down to few mK. PPMS system is designed to measure the physical properties of materials in bulk, thin film, and powder form.
X-Ray Diffractometer(XRD)
X-Ray diffraction is a technique used to determine the atomic and molecular structure of materials. In crystal, atoms are placed align with each other and they have regular spacing where this spacing is about 10 A. The general process that happens in XRD is look exactly like diffraction. The wavelength of the visible light is about 400 - 700 nm which is way bigger than the crystal spacing so we can not have this diffraction in the crystal with the visible light. However, if we can find a wavelength comparable to the atomic spacing 10 -10 m we can get a lot of information about the crystal by having the reflection in the crystal. As a matter of fact, x-ray light has this similar wavelength and this whole process is called X-Ray diffraction. Note that, we only get x-ray diffraction in the crystalline structure and there is no diffraction pattern for amorphous structures since they don't have any regular spacing.
Read more on XRD and the theories related to diffraction.
SQUID magnetometer
A SQUID (superconducting quantum interference device) is a very sensitive magnetometer used to measure extremely subtle magnetic fields, based on superconducting loops containing Josephson junctions. SQUIDs are sensitive enough to measure fields as low as 5×10−14 T with a few days of averaged measurements. The mechanism of SQUID magnetometer is explained in the diagram. The sample is shown as green which has some magnetization (a dipole field is shown in the figure). The sample is put on the rod and it put up and down through the coil, it generates current in the coil because there is a change in flux associated with this coil. There is a SQUID loop fat away from this region and through the flux transformer there are current which are induced in the pick-up coils. currents flow and generate the magnetic flux in the SQUID loop. The SQUID detects the magnetic flux and tells you how much current is present. The field that is generated in the SQUID loop is proportional to how much current is induced in the coil through which the magnetized sample is moving. In this way even a very weak magnetized samples which induced a very weak currents in pick-up coil can be detected using a SQUID magnetometer.
Hopefully you learned something new here. See you next time!